diff --git a/Libraries/BatchedBridge/BatchedBridge.js b/Libraries/BatchedBridge/BatchedBridge.js
index b68e9873e39..5b928edcc6b 100644
--- a/Libraries/BatchedBridge/BatchedBridge.js
+++ b/Libraries/BatchedBridge/BatchedBridge.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/BatchedBridge/MessageQueue.js b/Libraries/BatchedBridge/MessageQueue.js
index d68f2fd2cef..c1314d9ea79 100644
--- a/Libraries/BatchedBridge/MessageQueue.js
+++ b/Libraries/BatchedBridge/MessageQueue.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
@@ -22,7 +22,7 @@ export type SpyData = {
   type: number,
   module: ?string,
   method: string | number,
-  args: any[],
+  args: mixed[],
   ...
 };
 
@@ -40,10 +40,10 @@ const TRACE_TAG_REACT_APPS = 1 << 17;
 const DEBUG_INFO_LIMIT = 32;
 
 class MessageQueue {
-  _lazyCallableModules: {[key: string]: (void) => Object, ...};
-  _queue: [number[], number[], any[], number];
-  _successCallbacks: Map<number, ?Function>;
-  _failureCallbacks: Map<number, ?Function>;
+  _lazyCallableModules: {[key: string]: (void) => {...}, ...};
+  _queue: [number[], number[], mixed[], number];
+  _successCallbacks: Map<number, ?(...mixed[]) => void>;
+  _failureCallbacks: Map<number, ?(...mixed[]) => void>;
   _callID: number;
   _lastFlush: number;
   _eventLoopStartTime: number;
@@ -71,11 +71,15 @@ class MessageQueue {
       this._remoteMethodTable = {};
     }
 
-    (this: any).callFunctionReturnFlushedQueue = this.callFunctionReturnFlushedQueue.bind(
+    // $FlowFixMe[cannot-write]
+    this.callFunctionReturnFlushedQueue = this.callFunctionReturnFlushedQueue.bind(
       this,
     );
-    (this: any).flushedQueue = this.flushedQueue.bind(this);
-    (this: any).invokeCallbackAndReturnFlushedQueue = this.invokeCallbackAndReturnFlushedQueue.bind(
+    // $FlowFixMe[cannot-write]
+    this.flushedQueue = this.flushedQueue.bind(this);
+
+    // $FlowFixMe[cannot-write]
+    this.invokeCallbackAndReturnFlushedQueue = this.invokeCallbackAndReturnFlushedQueue.bind(
       this,
     );
   }
@@ -89,7 +93,7 @@ class MessageQueue {
       MessageQueue.prototype.__spy = info => {
         console.log(
           `${info.type === TO_JS ? 'N->JS' : 'JS->N'} : ` +
-            `${info.module ? info.module + '.' : ''}${info.method}` +
+            `${info.module != null ? info.module + '.' : ''}${info.method}` +
             `(${JSON.stringify(info.args)})`,
         );
       };
@@ -103,8 +107,8 @@ class MessageQueue {
   callFunctionReturnFlushedQueue(
     module: string,
     method: string,
-    args: any[],
-  ): null | [Array<number>, Array<number>, Array<any>, number] {
+    args: mixed[],
+  ): null | [Array<number>, Array<number>, Array<mixed>, number] {
     this.__guard(() => {
       this.__callFunction(module, method, args);
     });
@@ -114,8 +118,8 @@ class MessageQueue {
 
   invokeCallbackAndReturnFlushedQueue(
     cbID: number,
-    args: any[],
-  ): null | [Array<number>, Array<number>, Array<any>, number] {
+    args: mixed[],
+  ): null | [Array<number>, Array<number>, Array<mixed>, number] {
     this.__guard(() => {
       this.__invokeCallback(cbID, args);
     });
@@ -123,7 +127,7 @@ class MessageQueue {
     return this.flushedQueue();
   }
 
-  flushedQueue(): null | [Array<number>, Array<number>, Array<any>, number] {
+  flushedQueue(): null | [Array<number>, Array<number>, Array<mixed>, number] {
     this.__guard(() => {
       this.__callImmediates();
     });
@@ -137,13 +141,13 @@ class MessageQueue {
     return Date.now() - this._eventLoopStartTime;
   }
 
-  registerCallableModule(name: string, module: Object) {
+  registerCallableModule(name: string, module: {...}) {
     this._lazyCallableModules[name] = () => module;
   }
 
-  registerLazyCallableModule(name: string, factory: void => Object) {
-    let module: Object;
-    let getValue: ?(void) => Object = factory;
+  registerLazyCallableModule(name: string, factory: void => {...}) {
+    let module: {...};
+    let getValue: ?(void) => {...} = factory;
     this._lazyCallableModules[name] = () => {
       if (getValue) {
         module = getValue();
@@ -153,7 +157,7 @@ class MessageQueue {
     };
   }
 
-  getCallableModule(name: string): any | null {
+  getCallableModule(name: string): {...} | null {
     const getValue = this._lazyCallableModules[name];
     return getValue ? getValue() : null;
   }
@@ -161,10 +165,10 @@ class MessageQueue {
   callNativeSyncHook(
     moduleID: number,
     methodID: number,
-    params: any[],
-    onFail: ?Function,
-    onSucc: ?Function,
-  ): any {
+    params: mixed[],
+    onFail: ?(...mixed[]) => void,
+    onSucc: ?(...mixed[]) => void,
+  ): mixed {
     if (__DEV__) {
       invariant(
         global.nativeCallSyncHook,
@@ -181,10 +185,10 @@ class MessageQueue {
   processCallbacks(
     moduleID: number,
     methodID: number,
-    params: any[],
-    onFail: ?Function,
-    onSucc: ?Function,
-  ) {
+    params: mixed[],
+    onFail: ?(...mixed[]) => void,
+    onSucc: ?(...mixed[]) => void,
+  ): void {
     if (onFail || onSucc) {
       if (__DEV__) {
         this._debugInfo[this._callID] = [moduleID, methodID];
@@ -232,9 +236,9 @@ class MessageQueue {
   enqueueNativeCall(
     moduleID: number,
     methodID: number,
-    params: any[],
-    onFail: ?Function,
-    onSucc: ?Function,
+    params: mixed[],
+    onFail: ?(...mixed[]) => void,
+    onSucc: ?(...mixed[]) => void,
   ) {
     this.processCallbacks(moduleID, methodID, params, onFail, onSucc);
 
@@ -247,30 +251,34 @@ class MessageQueue {
       // function it is permitted here, and special-cased in the
       // conversion.
       const isValidArgument = val => {
-        const t = typeof val;
-        if (
-          t === 'undefined' ||
-          t === 'null' ||
-          t === 'boolean' ||
-          t === 'string'
-        ) {
-          return true;
-        }
-        if (t === 'number') {
-          return isFinite(val);
-        }
-        if (t === 'function' || t !== 'object') {
-          return false;
-        }
-        if (Array.isArray(val)) {
-          return val.every(isValidArgument);
-        }
-        for (const k in val) {
-          if (typeof val[k] !== 'function' && !isValidArgument(val[k])) {
+        switch (typeof val) {
+          case 'undefined':
+          case 'boolean':
+          case 'string':
+            return true;
+          case 'number':
+            return isFinite(val);
+          case 'object':
+            if (val == null) {
+              return true;
+            }
+
+            if (Array.isArray(val)) {
+              return val.every(isValidArgument);
+            }
+
+            for (const k in val) {
+              if (typeof val[k] !== 'function' && !isValidArgument(val[k])) {
+                return false;
+              }
+            }
+
+            return true;
+          case 'function':
+            return false;
+          default:
             return false;
-          }
         }
-        return true;
       };
 
       // Replacement allows normally non-JSON-convertible values to be
@@ -295,7 +303,7 @@ class MessageQueue {
       );
 
       // The params object should not be mutated after being queued
-      deepFreezeAndThrowOnMutationInDev((params: any));
+      deepFreezeAndThrowOnMutationInDev(params);
     }
     this._queue[PARAMS].push(params);
 
@@ -382,7 +390,7 @@ class MessageQueue {
     Systrace.endEvent();
   }
 
-  __callFunction(module: string, method: string, args: any[]): void {
+  __callFunction(module: string, method: string, args: mixed[]): void {
     this._lastFlush = Date.now();
     this._eventLoopStartTime = this._lastFlush;
     if (__DEV__ || this.__spy) {
@@ -410,7 +418,7 @@ class MessageQueue {
     Systrace.endEvent();
   }
 
-  __invokeCallback(cbID: number, args: any[]) {
+  __invokeCallback(cbID: number, args: mixed[]) {
     this._lastFlush = Date.now();
     this._eventLoopStartTime = this._lastFlush;
 
diff --git a/Libraries/BatchedBridge/NativeModules.js b/Libraries/BatchedBridge/NativeModules.js
index 541012582c0..4f764463738 100644
--- a/Libraries/BatchedBridge/NativeModules.js
+++ b/Libraries/BatchedBridge/NativeModules.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -18,7 +18,7 @@ import type {ExtendedError} from '../Core/Devtools/parseErrorStack';
 
 export type ModuleConfig = [
   string /* name */,
-  ?Object /* constants */,
+  ?{...} /* constants */,
   ?$ReadOnlyArray<string> /* functions */,
   ?$ReadOnlyArray<number> /* promise method IDs */,
   ?$ReadOnlyArray<number> /* sync method IDs */,
@@ -31,7 +31,7 @@ function genModule(
   moduleID: number,
 ): ?{
   name: string,
-  module?: Object,
+  module?: {...},
   ...
 } {
   if (!config) {
@@ -55,8 +55,9 @@ function genModule(
   methods &&
     methods.forEach((methodName, methodID) => {
       const isPromise =
-        promiseMethods && arrayContains(promiseMethods, methodID);
-      const isSync = syncMethods && arrayContains(syncMethods, methodID);
+        (promiseMethods && arrayContains(promiseMethods, methodID)) || false;
+      const isSync =
+        (syncMethods && arrayContains(syncMethods, methodID)) || false;
       invariant(
         !isPromise || !isSync,
         'Cannot have a method that is both async and a sync hook',
@@ -85,7 +86,7 @@ function genModule(
 // export this method as a global so we can call it from native
 global.__fbGenNativeModule = genModule;
 
-function loadModule(name: string, moduleID: number): ?Object {
+function loadModule(name: string, moduleID: number): ?{...} {
   invariant(
     global.nativeRequireModuleConfig,
     "Can't lazily create module without nativeRequireModuleConfig",
@@ -98,7 +99,7 @@ function loadModule(name: string, moduleID: number): ?Object {
 function genMethod(moduleID: number, methodID: number, type: MethodType) {
   let fn = null;
   if (type === 'promise') {
-    fn = function promiseMethodWrapper(...args: Array<any>) {
+    fn = function promiseMethodWrapper(...args: Array<mixed>) {
       // In case we reject, capture a useful stack trace here.
       const enqueueingFrameError: ExtendedError = new Error();
       return new Promise((resolve, reject) => {
@@ -108,12 +109,17 @@ function genMethod(moduleID: number, methodID: number, type: MethodType) {
           args,
           data => resolve(data),
           errorData =>
-            reject(updateErrorWithErrorData(errorData, enqueueingFrameError)),
+            reject(
+              updateErrorWithErrorData(
+                (errorData: $FlowFixMe),
+                enqueueingFrameError,
+              ),
+            ),
         );
       });
     };
   } else {
-    fn = function nonPromiseMethodWrapper(...args: Array<any>) {
+    fn = function nonPromiseMethodWrapper(...args: Array<mixed>) {
       const lastArg = args.length > 0 ? args[args.length - 1] : null;
       const secondLastArg = args.length > 1 ? args[args.length - 2] : null;
       const hasSuccessCallback = typeof lastArg === 'function';
@@ -123,15 +129,17 @@ function genMethod(moduleID: number, methodID: number, type: MethodType) {
           hasSuccessCallback,
           'Cannot have a non-function arg after a function arg.',
         );
-      const onSuccess = hasSuccessCallback ? lastArg : null;
-      const onFail = hasErrorCallback ? secondLastArg : null;
+      // $FlowFixMe[incompatible-type]
+      const onSuccess: ?(mixed) => void = hasSuccessCallback ? lastArg : null;
+      // $FlowFixMe[incompatible-type]
+      const onFail: ?(mixed) => void = hasErrorCallback ? secondLastArg : null;
       const callbackCount = hasSuccessCallback + hasErrorCallback;
-      args = args.slice(0, args.length - callbackCount);
+      const newArgs = args.slice(0, args.length - callbackCount);
       if (type === 'sync') {
         return BatchedBridge.callNativeSyncHook(
           moduleID,
           methodID,
-          args,
+          newArgs,
           onFail,
           onSuccess,
         );
@@ -139,7 +147,7 @@ function genMethod(moduleID: number, methodID: number, type: MethodType) {
         BatchedBridge.enqueueNativeCall(
           moduleID,
           methodID,
-          args,
+          newArgs,
           onFail,
           onSuccess,
         );
@@ -161,7 +169,7 @@ function updateErrorWithErrorData(
   return Object.assign(error, errorData || {});
 }
 
-let NativeModules: {[moduleName: string]: Object, ...} = {};
+let NativeModules: {[moduleName: string]: $FlowFixMe, ...} = {};
 if (global.nativeModuleProxy) {
   NativeModules = global.nativeModuleProxy;
 } else if (!global.nativeExtensions) {
diff --git a/Libraries/Blob/Blob.js b/Libraries/Blob/Blob.js
index 2af35f2bcb0..99d5e59b8e5 100644
--- a/Libraries/Blob/Blob.js
+++ b/Libraries/Blob/Blob.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
@@ -67,10 +67,12 @@ class Blob {
    * the data in the specified range of bytes of the source Blob.
    * Reference: https://developer.mozilla.org/en-US/docs/Web/API/Blob/slice
    */
+  // $FlowFixMe[unsafe-getters-setters]
   set data(data: ?BlobData) {
     this._data = data;
   }
 
+  // $FlowFixMe[unsafe-getters-setters]
   get data(): BlobData {
     if (!this._data) {
       throw new Error('Blob has been closed and is no longer available');
@@ -85,6 +87,7 @@ class Blob {
 
     if (typeof start === 'number') {
       if (start > size) {
+        // $FlowFixMe[reassign-const]
         start = size;
       }
       offset += start;
@@ -92,6 +95,7 @@ class Blob {
 
       if (typeof end === 'number') {
         if (end < 0) {
+          // $FlowFixMe[reassign-const]
           end = this.size + end;
         }
         size = end - start;
@@ -125,6 +129,7 @@ class Blob {
   /**
    * Size of the data contained in the Blob object, in bytes.
    */
+  // $FlowFixMe[unsafe-getters-setters]
   get size(): number {
     return this.data.size;
   }
@@ -133,6 +138,7 @@ class Blob {
    * String indicating the MIME type of the data contained in the Blob.
    * If the type is unknown, this string is empty.
    */
+  // $FlowFixMe[unsafe-getters-setters]
   get type(): string {
     return this.data.type || '';
   }
diff --git a/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js b/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js
index 3c77eb3c9f3..b0909d2b072 100644
--- a/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js
+++ b/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -90,6 +90,7 @@ const AccessibilityInfo = {
    *
    * Same as `isScreenReaderEnabled`
    */
+  // $FlowFixMe[unsafe-getters-setters]
   get fetch(): () => Promise<boolean> {
     console.warn(
       'AccessibilityInfo.fetch is deprecated, call AccessibilityInfo.isScreenReaderEnabled instead',
@@ -97,34 +98,27 @@ const AccessibilityInfo = {
     return this.isScreenReaderEnabled;
   },
 
-  addEventListener: function(
-    eventName: ChangeEventName,
-    handler: Function,
-  ): void {
+  addEventListener: function<T>(eventName: ChangeEventName, handler: T): void {
     let listener;
 
     if (eventName === 'change' || eventName === 'screenReaderChanged') {
       listener = RCTDeviceEventEmitter.addListener(
         TOUCH_EXPLORATION_EVENT,
-        enabled => {
-          handler(enabled);
-        },
+        handler,
       );
     } else if (eventName === 'reduceMotionChanged') {
       listener = RCTDeviceEventEmitter.addListener(
         REDUCE_MOTION_EVENT,
-        enabled => {
-          handler(enabled);
-        },
+        handler,
       );
     }
 
     _subscriptions.set(handler, listener);
   },
 
-  removeEventListener: function(
+  removeEventListener: function<T>(
     eventName: ChangeEventName,
-    handler: Function,
+    handler: T,
   ): void {
     const listener = _subscriptions.get(handler);
     if (!listener) {
diff --git a/Libraries/Components/AccessibilityInfo/AccessibilityInfo.ios.js b/Libraries/Components/AccessibilityInfo/AccessibilityInfo.ios.js
index 6df67ffaebb..fb73ab2ee24 100644
--- a/Libraries/Components/AccessibilityInfo/AccessibilityInfo.ios.js
+++ b/Libraries/Components/AccessibilityInfo/AccessibilityInfo.ios.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -163,6 +163,7 @@ const AccessibilityInfo = {
    *
    * Same as `isScreenReaderEnabled`
    */
+  // $FlowFixMe[unsafe-getters-setters]
   get fetch(): $FlowFixMe {
     console.warn(
       'AccessibilityInfo.fetch is deprecated, call AccessibilityInfo.isScreenReaderEnabled instead',
@@ -201,10 +202,10 @@ const AccessibilityInfo = {
    *
    * See https://reactnative.dev/docs/accessibilityinfo.html#addeventlistener
    */
-  addEventListener: function(
+  addEventListener: function<T>(
     eventName: ChangeEventName,
-    handler: Function,
-  ): Object {
+    handler: T,
+  ): {remove: () => void} {
     let listener;
 
     if (eventName === 'change') {
@@ -253,9 +254,9 @@ const AccessibilityInfo = {
    *
    * See https://reactnative.dev/docs/accessibilityinfo.html#removeeventlistener
    */
-  removeEventListener: function(
+  removeEventListener: function<T>(
     eventName: ChangeEventName,
-    handler: Function,
+    handler: T,
   ): void {
     const listener = _subscriptions.get(handler);
     if (!listener) {
diff --git a/Libraries/Components/AccessibilityInfo/NativeAccessibilityInfo.js b/Libraries/Components/AccessibilityInfo/NativeAccessibilityInfo.js
index 10aa0f110cd..03484f2158c 100644
--- a/Libraries/Components/AccessibilityInfo/NativeAccessibilityInfo.js
+++ b/Libraries/Components/AccessibilityInfo/NativeAccessibilityInfo.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/AppleTV/NativeTVNavigationEventEmitter.js b/Libraries/Components/AppleTV/NativeTVNavigationEventEmitter.js
index 3cecc6e84e7..26f9f801679 100644
--- a/Libraries/Components/AppleTV/NativeTVNavigationEventEmitter.js
+++ b/Libraries/Components/AppleTV/NativeTVNavigationEventEmitter.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/Clipboard/Clipboard.js b/Libraries/Components/Clipboard/Clipboard.js
index d58b2285473..fa0b9a050d4 100644
--- a/Libraries/Components/Clipboard/Clipboard.js
+++ b/Libraries/Components/Clipboard/Clipboard.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/Clipboard/NativeClipboard.js b/Libraries/Components/Clipboard/NativeClipboard.js
index 35bfa11851c..b585a108e04 100644
--- a/Libraries/Components/Clipboard/NativeClipboard.js
+++ b/Libraries/Components/Clipboard/NativeClipboard.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/Keyboard/NativeKeyboardObserver.js b/Libraries/Components/Keyboard/NativeKeyboardObserver.js
index b6ef87b4d3a..7f077c3c88b 100644
--- a/Libraries/Components/Keyboard/NativeKeyboardObserver.js
+++ b/Libraries/Components/Keyboard/NativeKeyboardObserver.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/Sound/NativeSoundManager.js b/Libraries/Components/Sound/NativeSoundManager.js
index b5b72ac4959..d278168552f 100644
--- a/Libraries/Components/Sound/NativeSoundManager.js
+++ b/Libraries/Components/Sound/NativeSoundManager.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/Sound/SoundManager.js b/Libraries/Components/Sound/SoundManager.js
index 943b4c5c535..0e63332728f 100644
--- a/Libraries/Components/Sound/SoundManager.js
+++ b/Libraries/Components/Sound/SoundManager.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/StatusBar/NativeStatusBarManagerAndroid.js b/Libraries/Components/StatusBar/NativeStatusBarManagerAndroid.js
index ee25f79cf37..5b00b2a4c21 100644
--- a/Libraries/Components/StatusBar/NativeStatusBarManagerAndroid.js
+++ b/Libraries/Components/StatusBar/NativeStatusBarManagerAndroid.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/StatusBar/NativeStatusBarManagerIOS.js b/Libraries/Components/StatusBar/NativeStatusBarManagerIOS.js
index 9840e3da2d4..b5da2851bf2 100644
--- a/Libraries/Components/StatusBar/NativeStatusBarManagerIOS.js
+++ b/Libraries/Components/StatusBar/NativeStatusBarManagerIOS.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/ToastAndroid/NativeToastAndroid.js b/Libraries/Components/ToastAndroid/NativeToastAndroid.js
index d4039be72f3..97f70204e9b 100644
--- a/Libraries/Components/ToastAndroid/NativeToastAndroid.js
+++ b/Libraries/Components/ToastAndroid/NativeToastAndroid.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/Devtools/getDevServer.js b/Libraries/Core/Devtools/getDevServer.js
index c60d0e51606..97c7c72468c 100644
--- a/Libraries/Core/Devtools/getDevServer.js
+++ b/Libraries/Core/Devtools/getDevServer.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -36,7 +36,7 @@ function getDevServer(): DevServerInfo {
   }
 
   return {
-    url: _cachedDevServerURL || FALLBACK,
+    url: _cachedDevServerURL ?? FALLBACK,
     fullBundleUrl: _cachedFullBundleURL,
     bundleLoadedFromServer: _cachedDevServerURL !== null,
   };
diff --git a/Libraries/Core/Devtools/openFileInEditor.js b/Libraries/Core/Devtools/openFileInEditor.js
index 4d52b3f4ff7..66dca4721b9 100644
--- a/Libraries/Core/Devtools/openFileInEditor.js
+++ b/Libraries/Core/Devtools/openFileInEditor.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Core/Devtools/openURLInBrowser.js b/Libraries/Core/Devtools/openURLInBrowser.js
index e69dc57183f..d4b00663aaf 100644
--- a/Libraries/Core/Devtools/openURLInBrowser.js
+++ b/Libraries/Core/Devtools/openURLInBrowser.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Core/Devtools/parseErrorStack.js b/Libraries/Core/Devtools/parseErrorStack.js
index ec69f3f69cf..3df85895ab7 100644
--- a/Libraries/Core/Devtools/parseErrorStack.js
+++ b/Libraries/Core/Devtools/parseErrorStack.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Core/Devtools/parseHermesStack.js b/Libraries/Core/Devtools/parseHermesStack.js
index 7aa91caf5d3..9d3ba2f9284 100644
--- a/Libraries/Core/Devtools/parseHermesStack.js
+++ b/Libraries/Core/Devtools/parseHermesStack.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Core/Devtools/symbolicateStackTrace.js b/Libraries/Core/Devtools/symbolicateStackTrace.js
index ef128990867..7a6b8cd80ce 100644
--- a/Libraries/Core/Devtools/symbolicateStackTrace.js
+++ b/Libraries/Core/Devtools/symbolicateStackTrace.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -53,6 +53,7 @@ async function symbolicateStackTrace(
   // The fix below postpones trying to load fetch until the first call to symbolicateStackTrace.
   // At that time, we will have either global.fetch (whatwg-fetch) or RN's fetch.
   if (!fetch) {
+    // flowlint-next-line untyped-import:off
     fetch = global.fetch || require('../../Network/fetch').fetch;
   }
 
diff --git a/Libraries/Core/NativeExceptionsManager.js b/Libraries/Core/NativeExceptionsManager.js
index b47dc42f3e6..10b7b77e08e 100644
--- a/Libraries/Core/NativeExceptionsManager.js
+++ b/Libraries/Core/NativeExceptionsManager.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/ReactNativeVersion.js b/Libraries/Core/ReactNativeVersion.js
index 1fcb2e9eb61..67ca7cd62bc 100644
--- a/Libraries/Core/ReactNativeVersion.js
+++ b/Libraries/Core/ReactNativeVersion.js
@@ -6,7 +6,7 @@
  *
  * @format
  * @generated by scripts/bump-oss-version.js
- * @flow
+ * @flow strict
  */
 
 exports.version = {
diff --git a/Libraries/Core/ReactNativeVersionCheck.js b/Libraries/Core/ReactNativeVersionCheck.js
index 263d8794f0f..5958842b30f 100644
--- a/Libraries/Core/ReactNativeVersionCheck.js
+++ b/Libraries/Core/ReactNativeVersionCheck.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/SegmentFetcher/NativeSegmentFetcher.js b/Libraries/Core/SegmentFetcher/NativeSegmentFetcher.js
index 63df69cfbb3..8baeee3d4c1 100644
--- a/Libraries/Core/SegmentFetcher/NativeSegmentFetcher.js
+++ b/Libraries/Core/SegmentFetcher/NativeSegmentFetcher.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/Timers/NativeTiming.js b/Libraries/Core/Timers/NativeTiming.js
index 14d03d52cfd..53477dd6584 100644
--- a/Libraries/Core/Timers/NativeTiming.js
+++ b/Libraries/Core/Timers/NativeTiming.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/polyfillPromise.js b/Libraries/Core/polyfillPromise.js
index f7375ab1ee8..b15ccc2b301 100644
--- a/Libraries/Core/polyfillPromise.js
+++ b/Libraries/Core/polyfillPromise.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/setUpGlobals.js b/Libraries/Core/setUpGlobals.js
index 5acc42ae794..ea6da8fbbbe 100644
--- a/Libraries/Core/setUpGlobals.js
+++ b/Libraries/Core/setUpGlobals.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/setUpNavigator.js b/Libraries/Core/setUpNavigator.js
index 74f58695ad6..48cdd45cb1d 100644
--- a/Libraries/Core/setUpNavigator.js
+++ b/Libraries/Core/setUpNavigator.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/setUpPerformance.js b/Libraries/Core/setUpPerformance.js
index 6fd0a1e42b8..12cace05f81 100644
--- a/Libraries/Core/setUpPerformance.js
+++ b/Libraries/Core/setUpPerformance.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Core/setUpSystrace.js b/Libraries/Core/setUpSystrace.js
index dc50797f310..610324b440e 100644
--- a/Libraries/Core/setUpSystrace.js
+++ b/Libraries/Core/setUpSystrace.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/HeapCapture/HeapCapture.js b/Libraries/HeapCapture/HeapCapture.js
index 903343a05b0..d48368d8aa1 100644
--- a/Libraries/HeapCapture/HeapCapture.js
+++ b/Libraries/HeapCapture/HeapCapture.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/HeapCapture/NativeJSCHeapCapture.js b/Libraries/HeapCapture/NativeJSCHeapCapture.js
index 05e941f17e7..0605cd119e0 100644
--- a/Libraries/HeapCapture/NativeJSCHeapCapture.js
+++ b/Libraries/HeapCapture/NativeJSCHeapCapture.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Image/NativeImageEditor.js b/Libraries/Image/NativeImageEditor.js
index 19dbf3cb6e5..c6fdc63f7d4 100644
--- a/Libraries/Image/NativeImageEditor.js
+++ b/Libraries/Image/NativeImageEditor.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Image/NativeImagePickerIOS.js b/Libraries/Image/NativeImagePickerIOS.js
index 4db17f4059a..fa64998c57b 100644
--- a/Libraries/Image/NativeImagePickerIOS.js
+++ b/Libraries/Image/NativeImagePickerIOS.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Image/NativeImageStore.js b/Libraries/Image/NativeImageStore.js
index cbd7b22fd02..38603b6aaab 100644
--- a/Libraries/Image/NativeImageStore.js
+++ b/Libraries/Image/NativeImageStore.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Interaction/InteractionManager.js b/Libraries/Interaction/InteractionManager.js
index c438a67e7a9..8aec6727e33 100644
--- a/Libraries/Interaction/InteractionManager.js
+++ b/Libraries/Interaction/InteractionManager.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -88,13 +88,16 @@ const InteractionManager = {
   runAfterInteractions(
     task: ?Task,
   ): {
-    then: Function,
-    done: Function,
-    cancel: Function,
+    then: <U>(
+      onFulfill?: ?(void) => ?(Promise<U> | U),
+      onReject?: ?(error: mixed) => ?(Promise<U> | U),
+    ) => Promise<U>,
+    done: () => void,
+    cancel: () => void,
     ...
   } {
-    const tasks = [];
-    const promise = new Promise(resolve => {
+    const tasks: Array<Task> = [];
+    const promise = new Promise((resolve: () => void) => {
       _scheduleUpdate();
       if (task) {
         tasks.push(task);
@@ -164,8 +167,6 @@ let _nextUpdateHandle = 0;
 let _inc = 0;
 let _deadline = -1;
 
-declare function setImmediate(callback: any, ...args: Array<any>): number;
-
 /**
  * Schedule an asynchronous update to the interaction state.
  */
diff --git a/Libraries/Interaction/NativeFrameRateLogger.js b/Libraries/Interaction/NativeFrameRateLogger.js
index d248a7cf3cb..363294aed75 100644
--- a/Libraries/Interaction/NativeFrameRateLogger.js
+++ b/Libraries/Interaction/NativeFrameRateLogger.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 import type {TurboModule} from '../TurboModule/RCTExport';
diff --git a/Libraries/Interaction/TaskQueue.js b/Libraries/Interaction/TaskQueue.js
index 15eb69388dc..965953f64fb 100644
--- a/Libraries/Interaction/TaskQueue.js
+++ b/Libraries/Interaction/TaskQueue.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -16,14 +16,12 @@ const invariant = require('invariant');
 type SimpleTask = {
   name: string,
   run: () => void,
-  ...
 };
 type PromiseTask = {
   name: string,
-  gen: () => Promise<any>,
-  ...
+  gen: () => Promise<void>,
 };
-export type Task = Function | SimpleTask | PromiseTask;
+export type Task = SimpleTask | PromiseTask | (() => void);
 
 const DEBUG: false = false;
 
@@ -101,10 +99,10 @@ class TaskQueue {
     if (queue.length) {
       const task = queue.shift();
       try {
-        if (task.gen) {
+        if (typeof task === 'object' && task.gen) {
           DEBUG && infoLog('TaskQueue: genPromise for task ' + task.name);
-          this._genPromise((task: any)); // Rather than annoying tagged union
-        } else if (task.run) {
+          this._genPromise(task);
+        } else if (typeof task === 'object' && task.run) {
           DEBUG && infoLog('TaskQueue: run task ' + task.name);
           task.run();
         } else {
diff --git a/Libraries/JSInspector/InspectorAgent.js b/Libraries/JSInspector/InspectorAgent.js
index b3bd4613143..8c12d695293 100644
--- a/Libraries/JSInspector/InspectorAgent.js
+++ b/Libraries/JSInspector/InspectorAgent.js
@@ -5,12 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
 
-export type EventSender = (name: string, params: Object) => void;
+export type EventSender = (name: string, params: mixed) => void;
 
 class InspectorAgent {
   _eventSender: EventSender;
@@ -19,7 +19,7 @@ class InspectorAgent {
     this._eventSender = eventSender;
   }
 
-  sendEvent(name: string, params: Object) {
+  sendEvent(name: string, params: mixed) {
     this._eventSender(name, params);
   }
 }
diff --git a/Libraries/JSInspector/JSInspector.js b/Libraries/JSInspector/JSInspector.js
index 44917ac36b1..d4c8815ebe1 100644
--- a/Libraries/JSInspector/JSInspector.js
+++ b/Libraries/JSInspector/JSInspector.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/JSInspector/NetworkAgent.js b/Libraries/JSInspector/NetworkAgent.js
index 9f48f7cb1f2..f1811978709 100644
--- a/Libraries/JSInspector/NetworkAgent.js
+++ b/Libraries/JSInspector/NetworkAgent.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -22,7 +22,7 @@ type LoaderId = string;
 type FrameId = string;
 type Timestamp = number;
 
-type Headers = Object;
+type Headers = {[string]: string};
 
 // We don't currently care about this
 type ResourceTiming = null;
@@ -160,7 +160,7 @@ class Interceptor {
     return this._requests.get(requestId);
   }
 
-  requestSent(id: number, url: string, method: string, headers: Object) {
+  requestSent(id: number, url: string, method: string, headers: Headers) {
     const requestId = String(id);
     this._requests.set(requestId, '');
 
@@ -188,7 +188,7 @@ class Interceptor {
     this._agent.sendEvent('requestWillBeSent', event);
   }
 
-  responseReceived(id: number, url: string, status: number, headers: Object) {
+  responseReceived(id: number, url: string, status: number, headers: Headers) {
     const requestId = String(id);
     const response: Response = {
       url,
@@ -247,7 +247,7 @@ class Interceptor {
     this._agent.sendEvent('loadingFailed', event);
   }
 
-  _getMimeType(headers: Object): string {
+  _getMimeType(headers: Headers): string {
     const contentType = headers['Content-Type'] || '';
     return contentType.split(';')[0];
   }
diff --git a/Libraries/LayoutAnimation/LayoutAnimation.js b/Libraries/LayoutAnimation/LayoutAnimation.js
index 159b2b96c78..d68c0b14a04 100644
--- a/Libraries/LayoutAnimation/LayoutAnimation.js
+++ b/Libraries/LayoutAnimation/LayoutAnimation.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
@@ -23,9 +23,11 @@ import Platform from '../Utilities/Platform';
 // Reexport type
 export type LayoutAnimationConfig = LayoutAnimationConfig_;
 
+type OnAnimationDidEndCallback = () => void;
+
 function configureNext(
   config: LayoutAnimationConfig,
-  onAnimationDidEnd?: Function,
+  onAnimationDidEnd?: OnAnimationDidEndCallback,
 ) {
   if (!Platform.isTesting) {
     if (UIManager?.configureNextLayoutAnimation) {
@@ -131,13 +133,13 @@ const LayoutAnimation = {
   },
   Presets,
   easeInEaseOut: (configureNext.bind(null, Presets.easeInEaseOut): (
-    onAnimationDidEnd?: any,
+    onAnimationDidEnd?: OnAnimationDidEndCallback,
   ) => void),
   linear: (configureNext.bind(null, Presets.linear): (
-    onAnimationDidEnd?: any,
+    onAnimationDidEnd?: OnAnimationDidEndCallback,
   ) => void),
   spring: (configureNext.bind(null, Presets.spring): (
-    onAnimationDidEnd?: any,
+    onAnimationDidEnd?: OnAnimationDidEndCallback,
   ) => void),
 };
 
diff --git a/Libraries/Linking/Linking.js b/Libraries/Linking/Linking.js
index 7a0ab925a6d..1ce5a8ae079 100644
--- a/Libraries/Linking/Linking.js
+++ b/Libraries/Linking/Linking.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -33,7 +33,7 @@ class Linking extends NativeEventEmitter {
    *
    * See https://reactnative.dev/docs/linking.html#addeventlistener
    */
-  addEventListener(type: string, handler: Function) {
+  addEventListener<T>(type: string, handler: T) {
     this.addListener(type, handler);
   }
 
@@ -42,7 +42,7 @@ class Linking extends NativeEventEmitter {
    *
    * See https://reactnative.dev/docs/linking.html#removeeventlistener
    */
-  removeEventListener(type: string, handler: Function) {
+  removeEventListener<T>(type: string, handler: T) {
     this.removeListener(type, handler);
   }
 
@@ -51,7 +51,7 @@ class Linking extends NativeEventEmitter {
    *
    * See https://reactnative.dev/docs/linking.html#openurl
    */
-  openURL(url: string): Promise<any> {
+  openURL(url: string): Promise<void> {
     this._validateURL(url);
     return NativeLinking.openURL(url);
   }
@@ -71,7 +71,7 @@ class Linking extends NativeEventEmitter {
    *
    * See https://reactnative.dev/docs/linking.html#opensettings
    */
-  openSettings(): Promise<any> {
+  openSettings(): Promise<void> {
     return NativeLinking.openSettings();
   }
 
diff --git a/Libraries/Linking/NativeLinking.js b/Libraries/Linking/NativeLinking.js
index 18b3e7128cd..942aa4f01b8 100644
--- a/Libraries/Linking/NativeLinking.js
+++ b/Libraries/Linking/NativeLinking.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Modal/Modal.js b/Libraries/Modal/Modal.js
index caefe6a3dc5..89523ad5d9b 100644
--- a/Libraries/Modal/Modal.js
+++ b/Libraries/Modal/Modal.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -175,7 +175,7 @@ class Modal extends React.Component<Props> {
     if (
       props.presentationStyle &&
       props.presentationStyle !== 'overFullScreen' &&
-      props.transparent
+      props.transparent === true
     ) {
       console.warn(
         `Modal with '${props.presentationStyle}' presentation style and 'transparent' value is not supported.`,
@@ -189,7 +189,8 @@ class Modal extends React.Component<Props> {
     }
 
     const containerStyles = {
-      backgroundColor: this.props.transparent ? 'transparent' : 'white',
+      backgroundColor:
+        this.props.transparent === true ? 'transparent' : 'white',
     };
 
     let animationType = this.props.animationType || 'none';
@@ -197,7 +198,7 @@ class Modal extends React.Component<Props> {
     let presentationStyle = this.props.presentationStyle;
     if (!presentationStyle) {
       presentationStyle = 'fullScreen';
-      if (this.props.transparent) {
+      if (this.props.transparent === true) {
         presentationStyle = 'overFullScreen';
       }
     }
diff --git a/Libraries/Modal/NativeModalManager.js b/Libraries/Modal/NativeModalManager.js
index 159e095b9a4..05fc5b2c73c 100644
--- a/Libraries/Modal/NativeModalManager.js
+++ b/Libraries/Modal/NativeModalManager.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/NativeModules/specs/NativeAnimationsDebugModule.js b/Libraries/NativeModules/specs/NativeAnimationsDebugModule.js
index bb784a616cd..55c24c1f9d1 100644
--- a/Libraries/NativeModules/specs/NativeAnimationsDebugModule.js
+++ b/Libraries/NativeModules/specs/NativeAnimationsDebugModule.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/NativeModules/specs/NativeDevMenu.js b/Libraries/NativeModules/specs/NativeDevMenu.js
index 8d3880c739b..20b858a1c7d 100644
--- a/Libraries/NativeModules/specs/NativeDevMenu.js
+++ b/Libraries/NativeModules/specs/NativeDevMenu.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/NativeModules/specs/NativeDevSettings.js b/Libraries/NativeModules/specs/NativeDevSettings.js
index 48c155886cf..44acbd3a50b 100644
--- a/Libraries/NativeModules/specs/NativeDevSettings.js
+++ b/Libraries/NativeModules/specs/NativeDevSettings.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/NativeModules/specs/NativeDeviceEventManager.js b/Libraries/NativeModules/specs/NativeDeviceEventManager.js
index 342115dd0e4..775767e7275 100644
--- a/Libraries/NativeModules/specs/NativeDeviceEventManager.js
+++ b/Libraries/NativeModules/specs/NativeDeviceEventManager.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/NativeModules/specs/NativeDialogManagerAndroid.js b/Libraries/NativeModules/specs/NativeDialogManagerAndroid.js
index 4ca12692fa1..fcc476b3419 100644
--- a/Libraries/NativeModules/specs/NativeDialogManagerAndroid.js
+++ b/Libraries/NativeModules/specs/NativeDialogManagerAndroid.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/NativeModules/specs/NativeLogBox.js b/Libraries/NativeModules/specs/NativeLogBox.js
index 6d89481c390..782d1b078d4 100644
--- a/Libraries/NativeModules/specs/NativeLogBox.js
+++ b/Libraries/NativeModules/specs/NativeLogBox.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/NativeModules/specs/NativeSourceCode.js b/Libraries/NativeModules/specs/NativeSourceCode.js
index 903123c94da..b1fb30fc292 100644
--- a/Libraries/NativeModules/specs/NativeSourceCode.js
+++ b/Libraries/NativeModules/specs/NativeSourceCode.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Network/FormData.js b/Libraries/Network/FormData.js
index bdb1da311da..8ff36068869 100644
--- a/Libraries/Network/FormData.js
+++ b/Libraries/Network/FormData.js
@@ -5,12 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
 
-type FormDataValue = any;
+type FormDataValue = string | {name?: string, type?: string, uri: string};
 type FormDataNameValuePair = [string, FormDataValue];
 
 type Headers = {[name: string]: string, ...};
diff --git a/Libraries/Network/RCTNetworking.ios.js b/Libraries/Network/RCTNetworking.ios.js
index ec3706bf0ec..92ef3339431 100644
--- a/Libraries/Network/RCTNetworking.ios.js
+++ b/Libraries/Network/RCTNetworking.ios.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -25,7 +25,7 @@ class RCTNetworking extends NativeEventEmitter {
     method: string,
     trackingName: string,
     url: string,
-    headers: Object,
+    headers: {...},
     data: RequestBody,
     responseType: NativeResponseType,
     incrementalUpdates: boolean,
diff --git a/Libraries/Performance/NativeJSCSamplingProfiler.js b/Libraries/Performance/NativeJSCSamplingProfiler.js
index 519656d9d08..9ef08c96159 100644
--- a/Libraries/Performance/NativeJSCSamplingProfiler.js
+++ b/Libraries/Performance/NativeJSCSamplingProfiler.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Performance/PureComponentDebug.js b/Libraries/Performance/PureComponentDebug.js
index 982ed49353c..767a0d48727 100644
--- a/Libraries/Performance/PureComponentDebug.js
+++ b/Libraries/Performance/PureComponentDebug.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
@@ -27,7 +27,7 @@ opaque type DoNotCommitUsageOfPureComponentDebug = {...};
  */
 class PureComponentDebug<
   P: DoNotCommitUsageOfPureComponentDebug,
-  S: ?Object = void,
+  S: ?{...} = void,
 > extends React.Component<P, S> {
   shouldComponentUpdate(nextProps: P, nextState: S): boolean {
     const tag = this.constructor.name;
diff --git a/Libraries/Performance/SamplingProfiler.js b/Libraries/Performance/SamplingProfiler.js
index 2808f83ebdd..a1c0ece4d16 100644
--- a/Libraries/Performance/SamplingProfiler.js
+++ b/Libraries/Performance/SamplingProfiler.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Performance/Systrace.js b/Libraries/Performance/Systrace.js
index e1db39bbfc5..048c3d40427 100644
--- a/Libraries/Performance/Systrace.js
+++ b/Libraries/Performance/Systrace.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
@@ -138,11 +138,18 @@ const Systrace = {
   /**
    * beginEvent/endEvent for starting and then ending a profile within the same call stack frame
    **/
-  beginEvent(profileName?: any, args?: any) {
+  beginEvent(
+    profileName?: string | (() => string),
+    args?: {[string]: string, ...},
+  ) {
     if (_enabled) {
-      profileName =
+      const profileNameString =
         typeof profileName === 'function' ? profileName() : profileName;
-      global.nativeTraceBeginSection(TRACE_TAG_REACT_APPS, profileName, args);
+      global.nativeTraceBeginSection(
+        TRACE_TAG_REACT_APPS,
+        profileNameString,
+        args,
+      );
     }
   },
 
@@ -157,28 +164,28 @@ const Systrace = {
    * occur on another thread or out of the current stack frame, eg await
    * the returned cookie variable should be used as input into the endAsyncEvent call to end the profile
    **/
-  beginAsyncEvent(profileName?: any): any {
+  beginAsyncEvent(profileName?: string | (() => string)): number {
     const cookie = _asyncCookie;
     if (_enabled) {
       _asyncCookie++;
-      profileName =
+      const profileNameString =
         typeof profileName === 'function' ? profileName() : profileName;
       global.nativeTraceBeginAsyncSection(
         TRACE_TAG_REACT_APPS,
-        profileName,
+        profileNameString,
         cookie,
       );
     }
     return cookie;
   },
 
-  endAsyncEvent(profileName?: any, cookie?: any) {
+  endAsyncEvent(profileName?: string | (() => string), cookie?: number) {
     if (_enabled) {
-      profileName =
+      const profileNameString =
         typeof profileName === 'function' ? profileName() : profileName;
       global.nativeTraceEndAsyncSection(
         TRACE_TAG_REACT_APPS,
-        profileName,
+        profileNameString,
         cookie,
       );
     }
@@ -187,12 +194,16 @@ const Systrace = {
   /**
    * counterEvent registers the value to the profileName on the systrace timeline
    **/
-  counterEvent(profileName?: any, value?: any) {
+  counterEvent(profileName?: string | (() => string), value?: number) {
     if (_enabled) {
-      profileName =
+      const profileNameString =
         typeof profileName === 'function' ? profileName() : profileName;
       global.nativeTraceCounter &&
-        global.nativeTraceCounter(TRACE_TAG_REACT_APPS, profileName, value);
+        global.nativeTraceCounter(
+          TRACE_TAG_REACT_APPS,
+          profileNameString,
+          value,
+        );
     }
   },
 };
@@ -202,7 +213,7 @@ if (__DEV__) {
   // other files. Therefore, calls to `require('moduleId')` are not replaced
   // with numeric IDs
   // TODO(davidaurelio) Scan polyfills for dependencies, too (t9759686)
-  (require: any).Systrace = Systrace;
+  (require: $FlowFixMe).Systrace = Systrace;
 }
 
 module.exports = Systrace;
diff --git a/Libraries/PermissionsAndroid/NativePermissionsAndroid.js b/Libraries/PermissionsAndroid/NativePermissionsAndroid.js
index 14aba8f1116..2e834fc725c 100644
--- a/Libraries/PermissionsAndroid/NativePermissionsAndroid.js
+++ b/Libraries/PermissionsAndroid/NativePermissionsAndroid.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/PermissionsAndroid/PermissionsAndroid.js b/Libraries/PermissionsAndroid/PermissionsAndroid.js
index 83124ccc24b..d99ccd5ec83 100644
--- a/Libraries/PermissionsAndroid/PermissionsAndroid.js
+++ b/Libraries/PermissionsAndroid/PermissionsAndroid.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Pressability/HoverState.js b/Libraries/Pressability/HoverState.js
index df15f610993..ab9febf2b36 100644
--- a/Libraries/Pressability/HoverState.js
+++ b/Libraries/Pressability/HoverState.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Promise.js b/Libraries/Promise.js
index 292bc270744..836c2978a73 100644
--- a/Libraries/Promise.js
+++ b/Libraries/Promise.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -18,25 +18,29 @@ require('promise/setimmediate/finally');
 if (__DEV__) {
   require('promise/setimmediate/rejection-tracking').enable({
     allRejections: true,
-    onUnhandled: (id, error = {}) => {
+    onUnhandled: (id, rejection = {}) => {
       let message: string;
       let stack: ?string;
 
-      const stringValue = Object.prototype.toString.call(error);
+      const stringValue = Object.prototype.toString.call(rejection);
       if (stringValue === '[object Error]') {
-        message = Error.prototype.toString.call(error);
+        message = Error.prototype.toString.call(rejection);
+        const error: Error = (rejection: $FlowFixMe);
         stack = error.stack;
       } else {
         try {
-          message = require('pretty-format')(error);
+          message = require('pretty-format')(rejection);
         } catch {
-          message = typeof error === 'string' ? error : JSON.stringify(error);
+          message =
+            typeof rejection === 'string'
+              ? rejection
+              : JSON.stringify((rejection: $FlowFixMe));
         }
       }
 
       const warning =
         `Possible Unhandled Promise Rejection (id: ${id}):\n` +
-        `${message}\n` +
+        `${message ?? ''}\n` +
         (stack == null ? '' : stack);
       console.warn(warning);
     },
diff --git a/Libraries/ReactNative/NativeHeadlessJsTaskSupport.js b/Libraries/ReactNative/NativeHeadlessJsTaskSupport.js
index 8cd05cf3afb..45f25deb211 100644
--- a/Libraries/ReactNative/NativeHeadlessJsTaskSupport.js
+++ b/Libraries/ReactNative/NativeHeadlessJsTaskSupport.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/ReactNative/NativeI18nManager.js b/Libraries/ReactNative/NativeI18nManager.js
index e16db811e62..28933d510b3 100644
--- a/Libraries/ReactNative/NativeI18nManager.js
+++ b/Libraries/ReactNative/NativeI18nManager.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/ReactNative/UIManagerProperties.js b/Libraries/ReactNative/UIManagerProperties.js
index 938e42eef9d..77e67267e57 100644
--- a/Libraries/ReactNative/UIManagerProperties.js
+++ b/Libraries/ReactNative/UIManagerProperties.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Share/NativeShareModule.js b/Libraries/Share/NativeShareModule.js
index 88293b8ce87..08d313d76d7 100644
--- a/Libraries/Share/NativeShareModule.js
+++ b/Libraries/Share/NativeShareModule.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Share/Share.js b/Libraries/Share/Share.js
index aed341e56d0..5dad4772b7e 100644
--- a/Libraries/Share/Share.js
+++ b/Libraries/Share/Share.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -74,7 +74,10 @@ class Share {
    *  - `dialogTitle`
    *
    */
-  static share(content: Content, options: Options = {}): Promise<Object> {
+  static share(
+    content: Content,
+    options: Options = {},
+  ): Promise<{action: string, activityType: ?string}> {
     invariant(
       typeof content === 'object' && content !== null,
       'Content to share must be a valid object',
@@ -94,7 +97,7 @@ class Share {
         'ShareModule should be registered on Android.',
       );
       invariant(
-        !content.title || typeof content.title === 'string',
+        content.title == null || typeof content.title === 'string',
         'Invalid title: title should be a string.',
       );
 
@@ -104,7 +107,12 @@ class Share {
           typeof content.message === 'string' ? content.message : undefined,
       };
 
-      return NativeShareModule.share(newContent, options.dialogTitle);
+      return NativeShareModule.share(newContent, options.dialogTitle).then(
+        result => ({
+          activityType: null,
+          ...result,
+        }),
+      );
     } else if (Platform.OS === 'ios') {
       return new Promise((resolve, reject) => {
         const tintColor = processColor(options.tintColor);
@@ -138,6 +146,7 @@ class Share {
             } else {
               resolve({
                 action: 'dismissedAction',
+                activityType: null,
               });
             }
           },
diff --git a/Libraries/Storage/NativeAsyncStorage.js b/Libraries/Storage/NativeAsyncStorage.js
index c67d291d034..539adfd80dc 100644
--- a/Libraries/Storage/NativeAsyncStorage.js
+++ b/Libraries/Storage/NativeAsyncStorage.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/TurboModule/TurboModuleRegistry.js b/Libraries/TurboModule/TurboModuleRegistry.js
index b3b1135f98b..1f06b8271a6 100644
--- a/Libraries/TurboModule/TurboModuleRegistry.js
+++ b/Libraries/TurboModule/TurboModuleRegistry.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
@@ -22,7 +22,7 @@ export function get<T: TurboModule>(name: string): ?T {
     // Backward compatibility layer during migration.
     const legacyModule = NativeModules[name];
     if (legacyModule != null) {
-      return ((legacyModule: any): T);
+      return ((legacyModule: $FlowFixMe): T);
     }
   }
 
diff --git a/Libraries/UTFSequence.js b/Libraries/UTFSequence.js
index 70d17a3ba40..65a548df756 100644
--- a/Libraries/UTFSequence.js
+++ b/Libraries/UTFSequence.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/Appearance.js b/Libraries/Utilities/Appearance.js
index b63ff33c700..314b3eaaad6 100644
--- a/Libraries/Utilities/Appearance.js
+++ b/Libraries/Utilities/Appearance.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
diff --git a/Libraries/Utilities/BackHandler.android.js b/Libraries/Utilities/BackHandler.android.js
index ed5bb00d96a..e762c1635f9 100644
--- a/Libraries/Utilities/BackHandler.android.js
+++ b/Libraries/Utilities/BackHandler.android.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
diff --git a/Libraries/Utilities/BackHandler.ios.js b/Libraries/Utilities/BackHandler.ios.js
index f7ed0515f2d..1407a57e95f 100644
--- a/Libraries/Utilities/BackHandler.ios.js
+++ b/Libraries/Utilities/BackHandler.ios.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
@@ -111,12 +111,15 @@ if (Platform.isTV) {
 } else {
   BackHandler = {
     exitApp: emptyFunction,
-    addEventListener(_eventName: BackPressEventName, _handler: Function) {
+    addEventListener(_eventName: BackPressEventName, _handler: () => ?boolean) {
       return {
         remove: emptyFunction,
       };
     },
-    removeEventListener(_eventName: BackPressEventName, _handler: Function) {},
+    removeEventListener(
+      _eventName: BackPressEventName,
+      _handler: () => ?boolean,
+    ) {},
   };
 }
 
diff --git a/Libraries/Utilities/DevSettings.js b/Libraries/Utilities/DevSettings.js
index 42ffec85148..58494938ec6 100644
--- a/Libraries/Utilities/DevSettings.js
+++ b/Libraries/Utilities/DevSettings.js
@@ -5,12 +5,19 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
+ * @flow strict-local
  */
 
 import NativeDevSettings from '../NativeModules/specs/NativeDevSettings';
 import NativeEventEmitter from '../EventEmitter/NativeEventEmitter';
 
-class DevSettings extends NativeEventEmitter {
+interface IDevSettings {
+  addMenuItem(title: string, handler: () => mixed): void;
+  reload(reason?: string): void;
+  onFastRefresh(): void;
+}
+
+class DevSettings extends NativeEventEmitter implements IDevSettings {
   _menuItems: Map<string, () => mixed>;
 
   constructor() {
@@ -39,9 +46,9 @@ class DevSettings extends NativeEventEmitter {
     });
   }
 
-  reload(reason: string) {
+  reload(reason?: string) {
     if (typeof NativeDevSettings.reloadWithReason === 'function') {
-      NativeDevSettings.reloadWithReason(reason || 'Uncategorized from JS');
+      NativeDevSettings.reloadWithReason(reason ?? 'Uncategorized from JS');
     } else {
       NativeDevSettings.reload();
     }
@@ -57,9 +64,12 @@ class DevSettings extends NativeEventEmitter {
 }
 
 // Avoid including the full `NativeDevSettings` class in prod.
-class NoopDevSettings {
+class NoopDevSettings implements IDevSettings {
   addMenuItem(title: string, handler: () => mixed) {}
-  reload() {}
+  reload(reason?: string) {}
+  onFastRefresh() {}
 }
 
-module.exports = __DEV__ ? new DevSettings() : new NoopDevSettings();
+module.exports = ((__DEV__
+  ? new DevSettings()
+  : new NoopDevSettings()): IDevSettings);
diff --git a/Libraries/Utilities/GlobalPerformanceLogger.js b/Libraries/Utilities/GlobalPerformanceLogger.js
index dedce0d110f..32ca41728bc 100644
--- a/Libraries/Utilities/GlobalPerformanceLogger.js
+++ b/Libraries/Utilities/GlobalPerformanceLogger.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/HMRClient.js b/Libraries/Utilities/HMRClient.js
index cf5d8eb54f6..7f00117793d 100644
--- a/Libraries/Utilities/HMRClient.js
+++ b/Libraries/Utilities/HMRClient.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 'use strict';
@@ -271,7 +271,7 @@ function setHMRUnavailableReason(reason) {
 }
 
 function registerBundleEntryPoints(client) {
-  if (hmrUnavailableReason) {
+  if (hmrUnavailableReason != null) {
     DevSettings.reload('Bundle Splitting – Metro disconnected');
     return;
   }
diff --git a/Libraries/Utilities/NativeAppearance.js b/Libraries/Utilities/NativeAppearance.js
index 5d37b8aded3..1f85cc30284 100644
--- a/Libraries/Utilities/NativeAppearance.js
+++ b/Libraries/Utilities/NativeAppearance.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/NativeDevLoadingView.js b/Libraries/Utilities/NativeDevLoadingView.js
index 8938fb6df5c..a122e2c487d 100644
--- a/Libraries/Utilities/NativeDevLoadingView.js
+++ b/Libraries/Utilities/NativeDevLoadingView.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/NativeDevSplitBundleLoader.js b/Libraries/Utilities/NativeDevSplitBundleLoader.js
index 505ae1c2108..987d47a5330 100644
--- a/Libraries/Utilities/NativeDevSplitBundleLoader.js
+++ b/Libraries/Utilities/NativeDevSplitBundleLoader.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/NativeDeviceInfo.js b/Libraries/Utilities/NativeDeviceInfo.js
index e1f2a6625de..840b754414c 100644
--- a/Libraries/Utilities/NativeDeviceInfo.js
+++ b/Libraries/Utilities/NativeDeviceInfo.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/NativeJSDevSupport.js b/Libraries/Utilities/NativeJSDevSupport.js
index 0c140f0f962..e609e1358ae 100644
--- a/Libraries/Utilities/NativeJSDevSupport.js
+++ b/Libraries/Utilities/NativeJSDevSupport.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/NativePlatformConstantsAndroid.js b/Libraries/Utilities/NativePlatformConstantsAndroid.js
index 39aa25d8c49..c12339267e5 100644
--- a/Libraries/Utilities/NativePlatformConstantsAndroid.js
+++ b/Libraries/Utilities/NativePlatformConstantsAndroid.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/NativePlatformConstantsIOS.js b/Libraries/Utilities/NativePlatformConstantsIOS.js
index fd73bcffadb..5b9d68bbc75 100644
--- a/Libraries/Utilities/NativePlatformConstantsIOS.js
+++ b/Libraries/Utilities/NativePlatformConstantsIOS.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Utilities/Platform.android.js b/Libraries/Utilities/Platform.android.js
index 3785bc8790a..ece5fe511ad 100644
--- a/Libraries/Utilities/Platform.android.js
+++ b/Libraries/Utilities/Platform.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -22,9 +22,11 @@ export type PlatformSelectSpec<A, N, D> = {
 const Platform = {
   __constants: null,
   OS: 'android',
+  // $FlowFixMe[unsafe-getters-setters]
   get Version(): number {
     return this.constants.Version;
   },
+  // $FlowFixMe[unsafe-getters-setters]
   get constants(): {|
     isTesting: boolean,
     reactNativeVersion: {|
@@ -46,12 +48,14 @@ const Platform = {
     }
     return this.__constants;
   },
+  // $FlowFixMe[unsafe-getters-setters]
   get isTesting(): boolean {
     if (__DEV__) {
       return this.constants.isTesting;
     }
     return false;
   },
+  // $FlowFixMe[unsafe-getters-setters]
   get isTV(): boolean {
     return this.constants.uiMode === 'tv';
   },
diff --git a/Libraries/Utilities/Platform.ios.js b/Libraries/Utilities/Platform.ios.js
index 2b8afec73e4..afb39c5aad8 100644
--- a/Libraries/Utilities/Platform.ios.js
+++ b/Libraries/Utilities/Platform.ios.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -22,9 +22,11 @@ export type PlatformSelectSpec<D, N, I> = {
 const Platform = {
   __constants: null,
   OS: 'ios',
+  // $FlowFixMe[unsafe-getters-setters]
   get Version(): string {
     return this.constants.osVersion;
   },
+  // $FlowFixMe[unsafe-getters-setters]
   get constants(): {|
     forceTouchAvailable: boolean,
     interfaceIdiom: string,
@@ -43,18 +45,22 @@ const Platform = {
     }
     return this.__constants;
   },
+  // $FlowFixMe[unsafe-getters-setters]
   get isPad(): boolean {
     return this.constants.interfaceIdiom === 'pad';
   },
   /**
    * Deprecated, use `isTV` instead.
    */
+  // $FlowFixMe[unsafe-getters-setters]
   get isTVOS(): boolean {
     return Platform.isTV;
   },
+  // $FlowFixMe[unsafe-getters-setters]
   get isTV(): boolean {
     return this.constants.interfaceIdiom === 'tv';
   },
+  // $FlowFixMe[unsafe-getters-setters]
   get isTesting(): boolean {
     if (__DEV__) {
       return this.constants.isTesting;
diff --git a/Libraries/Utilities/PolyfillFunctions.js b/Libraries/Utilities/PolyfillFunctions.js
index dc6d5a0fbcc..9dd136f593f 100644
--- a/Libraries/Utilities/PolyfillFunctions.js
+++ b/Libraries/Utilities/PolyfillFunctions.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
@@ -26,7 +26,7 @@ const defineLazyObjectProperty = require('./defineLazyObjectProperty');
  * @see https://github.com/facebook/react-native/issues/934
  */
 function polyfillObjectProperty<T>(
-  object: Object,
+  object: {...},
   name: string,
   getValue: () => T,
 ): void {
@@ -36,7 +36,7 @@ function polyfillObjectProperty<T>(
     Object.defineProperty(object, backupName, descriptor);
   }
 
-  const {enumerable, writable, configurable} = descriptor || {};
+  const {enumerable, writable, configurable = false} = descriptor || {};
   if (descriptor && !configurable) {
     console.error('Failed to set polyfill. ' + name + ' is not configurable.');
     return;
diff --git a/Libraries/Utilities/RCTLog.js b/Libraries/Utilities/RCTLog.js
index def04d6c3b2..78679c1f479 100644
--- a/Libraries/Utilities/RCTLog.js
+++ b/Libraries/Utilities/RCTLog.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -20,11 +20,11 @@ const levelsMap = {
   fatal: 'error',
 };
 
-let warningHandler: ?(Array<any>) => void = null;
+let warningHandler: ?(...Array<mixed>) => void = null;
 
 const RCTLog = {
   // level one of log, info, warn, error, mustfix
-  logIfNoNativeHook(level: string, ...args: Array<any>): void {
+  logIfNoNativeHook(level: string, ...args: Array<mixed>): void {
     // We already printed in the native console, so only log here if using a js debugger
     if (typeof global.nativeLoggingHook === 'undefined') {
       RCTLog.logToConsole(level, ...args);
@@ -37,7 +37,7 @@ const RCTLog = {
   },
 
   // Log to console regardless of nativeLoggingHook
-  logToConsole(level: string, ...args: Array<any>): void {
+  logToConsole(level: string, ...args: Array<mixed>): void {
     const logFn = levelsMap[level];
     invariant(
       logFn,
diff --git a/Libraries/Utilities/binaryToBase64.js b/Libraries/Utilities/binaryToBase64.js
index 19d23d125d2..8ae743553b7 100644
--- a/Libraries/Utilities/binaryToBase64.js
+++ b/Libraries/Utilities/binaryToBase64.js
@@ -5,15 +5,16 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
 
 const base64 = require('base64-js');
 
-function binaryToBase64(data: ArrayBuffer | $ArrayBufferView): any {
+function binaryToBase64(data: ArrayBuffer | $ArrayBufferView): string {
   if (data instanceof ArrayBuffer) {
+    // $FlowFixMe[reassign-const]
     data = new Uint8Array(data);
   }
   if (data instanceof Uint8Array) {
@@ -22,7 +23,8 @@ function binaryToBase64(data: ArrayBuffer | $ArrayBufferView): any {
   if (!ArrayBuffer.isView(data)) {
     throw new Error('data must be ArrayBuffer or typed array');
   }
-  const {buffer, byteOffset, byteLength} = data;
+  // Already checked that `data` is `DataView` in `ArrayBuffer.isView(data)`
+  const {buffer, byteOffset, byteLength} = ((data: $FlowFixMe): DataView);
   return base64.fromByteArray(new Uint8Array(buffer, byteOffset, byteLength));
 }
 
diff --git a/Libraries/Utilities/codegenNativeComponent.js b/Libraries/Utilities/codegenNativeComponent.js
index 809cdce1965..8376d9b4032 100644
--- a/Libraries/Utilities/codegenNativeComponent.js
+++ b/Libraries/Utilities/codegenNativeComponent.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict-local
  */
 
 // TODO: move this file to shims/ReactNative (requires React update and sync)
@@ -31,7 +31,7 @@ function codegenNativeComponent<Props>(
   options?: Options,
 ): NativeComponentType<Props> {
   let componentNameInUse =
-    options && options.paperComponentName
+    options && options.paperComponentName != null
       ? options.paperComponentName
       : componentName;
 
@@ -45,7 +45,7 @@ function codegenNativeComponent<Props>(
       componentNameInUse = options.paperComponentNameDeprecated;
     } else {
       throw new Error(
-        `Failed to find native component for either ${componentName} or ${options.paperComponentNameDeprecated ||
+        `Failed to find native component for either ${componentName} or ${options.paperComponentNameDeprecated ??
           '(unknown)'}`,
       );
     }
diff --git a/Libraries/Utilities/createPerformanceLogger.js b/Libraries/Utilities/createPerformanceLogger.js
index 556363a5fa4..927cb54e8b3 100644
--- a/Libraries/Utilities/createPerformanceLogger.js
+++ b/Libraries/Utilities/createPerformanceLogger.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
@@ -35,9 +35,9 @@ export type IPerformanceLogger = {
   hasTimespan(string): boolean,
   logTimespans(): void,
   addTimespans(Array<number>, Array<string>): void,
-  setExtra(string, any): void,
-  getExtras(): {[key: string]: any, ...},
-  removeExtra(string): ?any,
+  setExtra(string, mixed): void,
+  getExtras(): {[key: string]: mixed, ...},
+  removeExtra(string): ?mixed,
   logExtras(): void,
   markPoint(string, number | void): void,
   getPoints(): {[key: string]: number, ...},
@@ -58,7 +58,7 @@ const PRINT_TO_CONSOLE: false = false; // Type as false to prevent accidentally
 function createPerformanceLogger(): IPerformanceLogger {
   const result: IPerformanceLogger & {
     _timespans: {[key: string]: Timespan, ...},
-    _extras: {[key: string]: any, ...},
+    _extras: {[key: string]: mixed, ...},
     _points: {[key: string]: number, ...},
     ...
   } = {
@@ -206,7 +206,7 @@ function createPerformanceLogger(): IPerformanceLogger {
       }
     },
 
-    setExtra(key: string, value: any) {
+    setExtra(key: string, value: mixed) {
       if (this._extras[key]) {
         if (PRINT_TO_CONSOLE && __DEV__) {
           infoLog(
@@ -223,7 +223,7 @@ function createPerformanceLogger(): IPerformanceLogger {
       return this._extras;
     },
 
-    removeExtra(key: string): ?any {
+    removeExtra(key: string): ?mixed {
       const value = this._extras[key];
       delete this._extras[key];
       return value;
diff --git a/Libraries/Utilities/deepFreezeAndThrowOnMutationInDev.js b/Libraries/Utilities/deepFreezeAndThrowOnMutationInDev.js
index 974314539d2..72ddbe5cdda 100644
--- a/Libraries/Utilities/deepFreezeAndThrowOnMutationInDev.js
+++ b/Libraries/Utilities/deepFreezeAndThrowOnMutationInDev.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -27,7 +27,9 @@
  * Freezing the object and adding the throw mechanism is expensive and will
  * only be used in DEV.
  */
-function deepFreezeAndThrowOnMutationInDev<T: Object>(object: T): T {
+function deepFreezeAndThrowOnMutationInDev<T: {...} | Array<mixed>>(
+  object: T,
+): T {
   if (__DEV__) {
     if (
       typeof object !== 'object' ||
@@ -38,7 +40,8 @@ function deepFreezeAndThrowOnMutationInDev<T: Object>(object: T): T {
       return object;
     }
 
-    const keys = Object.keys(object);
+    // $FlowFixMe[not-an-object] `object` can be an array, but Object.keys works with arrays too
+    const keys = Object.keys((object: {...} | Array<mixed>));
     const hasOwnProperty = Object.prototype.hasOwnProperty;
 
     for (let i = 0; i < keys.length; i++) {
diff --git a/Libraries/Utilities/defineLazyObjectProperty.js b/Libraries/Utilities/defineLazyObjectProperty.js
index 9c5698a7036..c1b486a5fe4 100644
--- a/Libraries/Utilities/defineLazyObjectProperty.js
+++ b/Libraries/Utilities/defineLazyObjectProperty.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
@@ -14,7 +14,7 @@
  * Defines a lazily evaluated property on the supplied `object`.
  */
 function defineLazyObjectProperty<T>(
-  object: Object,
+  object: {...},
   name: string,
   descriptor: {
     get: () => T,
diff --git a/Libraries/Utilities/stringifySafe.js b/Libraries/Utilities/stringifySafe.js
index effeedcd299..e051f59f8f0 100644
--- a/Libraries/Utilities/stringifySafe.js
+++ b/Libraries/Utilities/stringifySafe.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Utilities/warnOnce.js b/Libraries/Utilities/warnOnce.js
index 70c7460c785..adbc64ebc85 100644
--- a/Libraries/Utilities/warnOnce.js
+++ b/Libraries/Utilities/warnOnce.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Vibration/NativeVibration.js b/Libraries/Vibration/NativeVibration.js
index 6de5352ec82..d2b2f2424e9 100644
--- a/Libraries/Vibration/NativeVibration.js
+++ b/Libraries/Vibration/NativeVibration.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict-local
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Vibration/Vibration.js b/Libraries/Vibration/Vibration.js
index 4a2d8444ea7..ab7f466be62 100644
--- a/Libraries/Vibration/Vibration.js
+++ b/Libraries/Vibration/Vibration.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  * @jsdoc
  */
 
@@ -31,6 +31,7 @@ function vibrateByPattern(pattern: Array<number>, repeat: boolean = false) {
   _vibrating = true;
   if (pattern[0] === 0) {
     NativeVibration.vibrate(_default_vibration_length);
+    // $FlowFixMe[reassign-const]
     pattern = pattern.slice(1);
   }
   if (pattern.length === 0) {
@@ -52,6 +53,7 @@ function vibrateScheduler(
   NativeVibration.vibrate(_default_vibration_length);
   if (nextIndex >= pattern.length) {
     if (repeat) {
+      // $FlowFixMe[reassign-const]
       nextIndex = 0;
     } else {
       _vibrating = false;
diff --git a/Libraries/promiseRejectionIsError.js b/Libraries/promiseRejectionIsError.js
index f17583d7b0c..2df61813e7b 100644
--- a/Libraries/promiseRejectionIsError.js
+++ b/Libraries/promiseRejectionIsError.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/flow-typed/npm/base64-js_v1.x.x.js b/flow-typed/npm/base64-js_v1.x.x.js
new file mode 100644
index 00000000000..8653866fdba
--- /dev/null
+++ b/flow-typed/npm/base64-js_v1.x.x.js
@@ -0,0 +1,14 @@
+/**
+ * (c) Facebook, Inc. and its affiliates. Confidential and proprietary.
+ *
+ * @flow strict
+ * @format
+ */
+
+declare module 'base64-js' {
+  declare module.exports: {
+    byteLength: string => number,
+    fromByteArray: (Uint8Array | Array<number>) => string,
+    toByteArray: string => Uint8Array,
+  };
+}
diff --git a/flow-typed/npm/pretty-format_v26.x.x.js b/flow-typed/npm/pretty-format_v26.x.x.js
new file mode 100644
index 00000000000..181d7909b34
--- /dev/null
+++ b/flow-typed/npm/pretty-format_v26.x.x.js
@@ -0,0 +1,51 @@
+/**
+ * (c) Facebook, Inc. and its affiliates. Confidential and proprietary.
+ *
+ * @flow strict
+ * @format
+ */
+
+type PrettyFormatPlugin =
+  | {
+      test: (value: mixed) => boolean,
+      print: (value: mixed) => string,
+    }
+  | {
+      test: (value: mixed) => boolean,
+      serialize: (value: mixed) => string,
+    };
+
+declare module 'pretty-format' {
+  declare module.exports: {
+    (
+      value: mixed,
+      options?: ?{
+        callToJSON?: ?boolean,
+        escapeRegex?: ?boolean,
+        escapeString?: ?boolean,
+        highlight?: ?boolean,
+        indent?: ?number,
+        maxDepth?: ?number,
+        min?: ?boolean,
+        plugins?: ?Array<PrettyFormatPlugin>,
+        printFunctionName?: ?boolean,
+        theme?: ?{
+          comment?: ?string,
+          prop?: ?string,
+          tag?: ?string,
+          value: ?string,
+        },
+      },
+    ): string,
+
+    plugins: {
+      AsymmetricMatcher: PrettyFormatPlugin,
+      ConvertAnsi: PrettyFormatPlugin,
+      DOMCollection: PrettyFormatPlugin,
+      DOMElement: PrettyFormatPlugin,
+      Immutable: PrettyFormatPlugin,
+      ReactElement: PrettyFormatPlugin,
+      ReactTestComponent: PrettyFormatPlugin,
+    },
+  };
+}
diff --git a/flow-typed/npm/promise_v8.x.x.js b/flow-typed/npm/promise_v8.x.x.js
new file mode 100644
index 00000000000..580f98cdd63
--- /dev/null
+++ b/flow-typed/npm/promise_v8.x.x.js
@@ -0,0 +1,32 @@
+/**
+ * (c) Facebook, Inc. and its affiliates. Confidential and proprietary.
+ *
+ * @flow strict
+ * @format
+ */
+
+declare module 'promise/setimmediate/es6-extensions' {
+  declare module.exports: Class<Promise>;
+}
+
+declare module 'promise/setimmediate/done' {
+  declare module.exports: Class<Promise>;
+}
+
+declare module 'promise/setimmediate/finally' {
+  declare module.exports: Class<Promise>;
+}
+
+declare module 'promise/setimmediate/rejection-tracking' {
+  declare module.exports: {
+    enable: (
+      options?: ?{
+        whitelist?: ?Array<mixed>,
+        allRejections?: ?boolean,
+        onUnhandled?: ?(number, mixed) => void,
+        onHandled?: ?(number, mixed) => void,
+      },
+    ) => void,
+    disable: () => void,
+  };
+}
diff --git a/flow-typed/npm/stacktrace-parser_v0.1.x.js b/flow-typed/npm/stacktrace-parser_v0.1.x.js
new file mode 100644
index 00000000000..9e990144531
--- /dev/null
+++ b/flow-typed/npm/stacktrace-parser_v0.1.x.js
@@ -0,0 +1,19 @@
+/**
+ * (c) Facebook, Inc. and its affiliates. Confidential and proprietary.
+ *
+ * @flow strict
+ * @format
+ */
+
+type StackFrame = {
+  file: string,
+  methodName: string,
+  lineNumber: number,
+  column: ?number,
+};
+
+declare module 'stacktrace-parser' {
+  declare module.exports: {
+    parse: string => Array<StackFrame>,
+  };
+}
diff --git a/scripts/versiontemplates/ReactNativeVersion.js.template b/scripts/versiontemplates/ReactNativeVersion.js.template
index 9e05c12fd81..72bfcfef110 100644
--- a/scripts/versiontemplates/ReactNativeVersion.js.template
+++ b/scripts/versiontemplates/ReactNativeVersion.js.template
@@ -6,7 +6,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  */
 
 exports.version = {