diff --git a/packages/legacy-events/EventSystemFlags.js b/packages/legacy-events/EventSystemFlags.js
index e31af6bae3..585519c117 100644
--- a/packages/legacy-events/EventSystemFlags.js
+++ b/packages/legacy-events/EventSystemFlags.js
@@ -11,10 +11,10 @@ export type EventSystemFlags = number;
 
 export const PLUGIN_EVENT_SYSTEM = 1;
 export const RESPONDER_EVENT_SYSTEM = 1 << 1;
-export const IS_PASSIVE = 1 << 2;
-export const IS_ACTIVE = 1 << 3;
-export const PASSIVE_NOT_SUPPORTED = 1 << 4;
-export const IS_REPLAYED = 1 << 5;
-export const IS_FIRST_ANCESTOR = 1 << 6;
-export const IS_TARGET_EVENT_ONLY = 1 << 7;
+export const USE_EVENT_SYSTEM = 1 << 2;
+export const IS_TARGET_PHASE_ONLY = 1 << 3;
+export const IS_PASSIVE = 1 << 4;
+export const PASSIVE_NOT_SUPPORTED = 1 << 5;
+export const IS_REPLAYED = 1 << 6;
+export const IS_FIRST_ANCESTOR = 1 << 7;
 export const LEGACY_FB_SUPPORT = 1 << 8;
diff --git a/packages/react-dom/src/__tests__/ReactDOM-test.js b/packages/react-dom/src/__tests__/ReactDOM-test.js
index c43ae76dc4..d8a6c6d2ff 100644
--- a/packages/react-dom/src/__tests__/ReactDOM-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOM-test.js
@@ -13,6 +13,7 @@ let React;
 let ReactDOM;
 let ReactDOMServer;
 let ReactTestUtils;
+const ReactFeatureFlags = require('shared/ReactFeatureFlags');
 
 describe('ReactDOM', () => {
   beforeEach(() => {
@@ -354,11 +355,31 @@ describe('ReactDOM', () => {
     document.body.appendChild(container);
     try {
       ReactDOM.render(<Wrapper />, container);
+      let expected;
+
+      if (
+        ReactFeatureFlags.enableModernEventSystem &
+        ReactFeatureFlags.enableLegacyFBSupport
+      ) {
+        // We expect to duplicate the 2nd handler because this test is
+        // not really designed around how the legacy FB support system works.
+        // This is because the above test sync fires a click() event
+        // during that of another click event, which causes the FB support system
+        // to duplicate adding an event listener. In practice this would never
+        // happen, as we only apply the legacy FB logic for "click" events,
+        // which would never stack this way in product code.
+        expected = [
+          '1st node clicked',
+          "2nd node clicked imperatively from 1st's handler",
+          "2nd node clicked imperatively from 1st's handler",
+        ];
+      } else {
+        expected = [
+          '1st node clicked',
+          "2nd node clicked imperatively from 1st's handler",
+        ];
+      }
 
-      const expected = [
-        '1st node clicked',
-        "2nd node clicked imperatively from 1st's handler",
-      ];
       expect(actual).toEqual(expected);
     } finally {
       document.body.removeChild(container);
diff --git a/packages/react-dom/src/__tests__/ReactDOMComponent-test.js b/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
index 49dc7a3b3c..d7e856f1a7 100644
--- a/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
@@ -14,6 +14,7 @@ describe('ReactDOMComponent', () => {
   let ReactTestUtils;
   let ReactDOM;
   let ReactDOMServer;
+  const ReactFeatureFlags = require('shared/ReactFeatureFlags');
 
   function normalizeCodeLocInfo(str) {
     return str && str.replace(/\(at .+?:\d+\)/g, '(at **)');
@@ -2595,14 +2596,30 @@ describe('ReactDOMComponent', () => {
       // might depend on this.
       //
       // @see https://github.com/facebook/react/pull/12919#issuecomment-395224674
-      expect(eventOrder).toEqual([
-        'document capture',
-        'inner capture',
-        'inner bubble',
-        'outer capture',
-        'outer bubble',
-        'document bubble',
-      ]);
+      if (
+        ReactFeatureFlags.enableModernEventSystem &
+        ReactFeatureFlags.enableLegacyFBSupport
+      ) {
+        // The order will change here, as the legacy FB support adds
+        // the event listener onto the document after the one above has.
+        expect(eventOrder).toEqual([
+          'document capture',
+          'document bubble',
+          'inner capture',
+          'inner bubble',
+          'outer capture',
+          'outer bubble',
+        ]);
+      } else {
+        expect(eventOrder).toEqual([
+          'document capture',
+          'inner capture',
+          'inner bubble',
+          'outer capture',
+          'outer bubble',
+          'document bubble',
+        ]);
+      }
     } finally {
       document.body.removeChild(container);
     }
diff --git a/packages/react-dom/src/client/ReactDOMHostConfig.js b/packages/react-dom/src/client/ReactDOMHostConfig.js
index 3927e3b61c..a8dae35dc8 100644
--- a/packages/react-dom/src/client/ReactDOMHostConfig.js
+++ b/packages/react-dom/src/client/ReactDOMHostConfig.js
@@ -76,6 +76,8 @@ import {HostComponent} from 'react-reconciler/src/ReactWorkTags';
 import {
   RESPONDER_EVENT_SYSTEM,
   IS_PASSIVE,
+  PLUGIN_EVENT_SYSTEM,
+  USE_EVENT_SYSTEM,
 } from 'legacy-events/EventSystemFlags';
 import {
   isManagedDOMElement,
@@ -1156,6 +1158,7 @@ export function registerEvent(
     type,
     rootContainerInstance,
     listenerMap,
+    PLUGIN_EVENT_SYSTEM | USE_EVENT_SYSTEM,
     passive,
     priority,
   );
diff --git a/packages/react-dom/src/events/DOMLegacyEventPluginSystem.js b/packages/react-dom/src/events/DOMLegacyEventPluginSystem.js
index 412d2c94aa..7a76374160 100644
--- a/packages/react-dom/src/events/DOMLegacyEventPluginSystem.js
+++ b/packages/react-dom/src/events/DOMLegacyEventPluginSystem.js
@@ -21,7 +21,10 @@ import {
   HostComponent,
   HostText,
 } from 'react-reconciler/src/ReactWorkTags';
-import {IS_FIRST_ANCESTOR} from 'legacy-events/EventSystemFlags';
+import {
+  IS_FIRST_ANCESTOR,
+  PLUGIN_EVENT_SYSTEM,
+} from 'legacy-events/EventSystemFlags';
 import {batchedEventUpdates} from 'legacy-events/ReactGenericBatching';
 import {runEventsInBatch} from 'legacy-events/EventBatching';
 import {plugins} from 'legacy-events/EventPluginRegistry';
@@ -372,7 +375,12 @@ export function legacyTrapBubbledEvent(
   element: Document | Element,
   listenerMap?: ElementListenerMap,
 ): void {
-  const listener = addTrappedEventListener(element, topLevelType, false);
+  const listener = addTrappedEventListener(
+    element,
+    topLevelType,
+    PLUGIN_EVENT_SYSTEM,
+    false,
+  );
   if (listenerMap) {
     listenerMap.set(topLevelType, {passive: undefined, listener});
   }
@@ -383,6 +391,11 @@ export function legacyTrapCapturedEvent(
   element: Document | Element,
   listenerMap: ElementListenerMap,
 ): void {
-  const listener = addTrappedEventListener(element, topLevelType, true);
+  const listener = addTrappedEventListener(
+    element,
+    topLevelType,
+    PLUGIN_EVENT_SYSTEM,
+    true,
+  );
   listenerMap.set(topLevelType, {passive: undefined, listener});
 }
diff --git a/packages/react-dom/src/events/DOMModernPluginEventSystem.js b/packages/react-dom/src/events/DOMModernPluginEventSystem.js
index 0816640e53..f5419c5a13 100644
--- a/packages/react-dom/src/events/DOMModernPluginEventSystem.js
+++ b/packages/react-dom/src/events/DOMModernPluginEventSystem.js
@@ -28,9 +28,11 @@ import {batchedEventUpdates} from 'legacy-events/ReactGenericBatching';
 import {executeDispatchesInOrder} from 'legacy-events/EventPluginUtils';
 import {plugins} from 'legacy-events/EventPluginRegistry';
 import {
+  PLUGIN_EVENT_SYSTEM,
   LEGACY_FB_SUPPORT,
   IS_REPLAYED,
-  IS_TARGET_EVENT_ONLY,
+  IS_TARGET_PHASE_ONLY,
+  USE_EVENT_SYSTEM,
 } from 'legacy-events/EventSystemFlags';
 
 import {HostRoot, HostPortal} from 'react-reconciler/src/ReactWorkTags';
@@ -229,6 +231,7 @@ export function listenToTopLevelEvent(
   topLevelType: DOMTopLevelEventType,
   targetContainer: EventTarget,
   listenerMap: ElementListenerMap,
+  eventSystemFlags: EventSystemFlags,
   passive?: boolean,
   priority?: EventPriority,
   capture?: boolean,
@@ -265,6 +268,7 @@ export function listenToTopLevelEvent(
     const listener = addTrappedEventListener(
       targetContainer,
       topLevelType,
+      eventSystemFlags,
       isCapturePhase,
       false,
       passive,
@@ -283,7 +287,12 @@ export function listenToEvent(
 
   for (let i = 0; i < dependencies.length; i++) {
     const dependency = dependencies[i];
-    listenToTopLevelEvent(dependency, rootContainerElement, listenerMap);
+    listenToTopLevelEvent(
+      dependency,
+      rootContainerElement,
+      listenerMap,
+      PLUGIN_EVENT_SYSTEM,
+    );
   }
 }
 
@@ -301,6 +310,7 @@ function willDeferLaterForLegacyFBSupport(
   addTrappedEventListener(
     targetContainer,
     topLevelType,
+    PLUGIN_EVENT_SYSTEM | LEGACY_FB_SUPPORT,
     false,
     isDeferredListenerForLegacyFBSupport,
   );
@@ -343,10 +353,9 @@ export function dispatchEventForPluginEventSystem(
 ): void {
   let ancestorInst = targetInst;
   if (targetContainer !== null) {
-    if (eventTargetEventListenerStore.has(targetContainer)) {
+    if (eventSystemFlags & IS_TARGET_PHASE_ONLY) {
       // For TargetEvent nodes (i.e. document, window)
       ancestorInst = null;
-      eventSystemFlags |= IS_TARGET_EVENT_ONLY;
     } else {
       const targetContainerNode = ((targetContainer: any): Node);
 
@@ -362,6 +371,8 @@ export function dispatchEventForPluginEventSystem(
         (eventSystemFlags & LEGACY_FB_SUPPORT) === 0 &&
         // We also don't want to defer during event replaying.
         (eventSystemFlags & IS_REPLAYED) === 0 &&
+        // We don't want to apply the legacy FB support for the useEvent API.
+        (eventSystemFlags & USE_EVENT_SYSTEM) === 0 &&
         willDeferLaterForLegacyFBSupport(topLevelType, targetContainer)
       ) {
         return;
@@ -483,6 +494,7 @@ export function attachListenerToManagedDOMElement(
     type,
     containerEventTarget,
     listenerMap,
+    PLUGIN_EVENT_SYSTEM | USE_EVENT_SYSTEM,
     passive,
     priority,
   );
@@ -522,6 +534,7 @@ export function attachTargetEventListener(listener: ReactDOMListener): void {
     type,
     eventTarget,
     listenerMap,
+    PLUGIN_EVENT_SYSTEM | USE_EVENT_SYSTEM | IS_TARGET_PHASE_ONLY,
     passive,
     priority,
     capture,
diff --git a/packages/react-dom/src/events/ReactDOMEventListener.js b/packages/react-dom/src/events/ReactDOMEventListener.js
index 02336d66cb..4b1bfd3830 100644
--- a/packages/react-dom/src/events/ReactDOMEventListener.js
+++ b/packages/react-dom/src/events/ReactDOMEventListener.js
@@ -37,12 +37,11 @@ import {
 import {HostRoot, SuspenseComponent} from 'react-reconciler/src/ReactWorkTags';
 import {
   type EventSystemFlags,
+  LEGACY_FB_SUPPORT,
   PLUGIN_EVENT_SYSTEM,
   RESPONDER_EVENT_SYSTEM,
   IS_PASSIVE,
-  IS_ACTIVE,
   PASSIVE_NOT_SUPPORTED,
-  LEGACY_FB_SUPPORT,
 } from 'legacy-events/EventSystemFlags';
 
 import {
@@ -103,12 +102,9 @@ export function addResponderEventSystemEvent(
     if (passiveBrowserEventsSupported) {
       eventFlags |= IS_PASSIVE;
     } else {
-      eventFlags |= IS_ACTIVE;
       eventFlags |= PASSIVE_NOT_SUPPORTED;
       passive = false;
     }
-  } else {
-    eventFlags |= IS_ACTIVE;
   }
   // Check if interactive and wrap in discreteUpdates
   const listener = dispatchEvent.bind(
@@ -132,6 +128,7 @@ export function addResponderEventSystemEvent(
 export function addTrappedEventListener(
   targetContainer: EventTarget,
   topLevelType: DOMTopLevelEventType,
+  eventSystemFlags: EventSystemFlags,
   capture: boolean,
   isDeferredListenerForLegacyFBSupport?: boolean,
   passive?: boolean,
@@ -160,10 +157,6 @@ export function addTrappedEventListener(
   if (passive === true && !passiveBrowserEventsSupported) {
     passive = false;
   }
-  const eventSystemFlags =
-    enableLegacyFBSupport && isDeferredListenerForLegacyFBSupport
-      ? PLUGIN_EVENT_SYSTEM | LEGACY_FB_SUPPORT
-      : PLUGIN_EVENT_SYSTEM;
 
   listener = listenerWrapper.bind(
     null,
@@ -268,7 +261,14 @@ function dispatchDiscreteEvent(
   container,
   nativeEvent,
 ) {
-  flushDiscreteUpdatesIfNeeded(nativeEvent.timeStamp);
+  if (
+    !enableLegacyFBSupport ||
+    // If we have Legacy FB support, it means we've already
+    // flushed for this event and we don't need to do it again.
+    (eventSystemFlags & LEGACY_FB_SUPPORT) === 0
+  ) {
+    flushDiscreteUpdatesIfNeeded(nativeEvent.timeStamp);
+  }
   discreteUpdates(
     dispatchEvent,
     topLevelType,
diff --git a/packages/react-dom/src/events/ReactDOMEventReplaying.js b/packages/react-dom/src/events/ReactDOMEventReplaying.js
index 4dc3874a20..9e39586ecf 100644
--- a/packages/react-dom/src/events/ReactDOMEventReplaying.js
+++ b/packages/react-dom/src/events/ReactDOMEventReplaying.js
@@ -118,7 +118,7 @@ import {
   TOP_FOCUS,
   TOP_BLUR,
 } from './DOMTopLevelEventTypes';
-import {IS_REPLAYED} from 'legacy-events/EventSystemFlags';
+import {IS_REPLAYED, PLUGIN_EVENT_SYSTEM} from 'legacy-events/EventSystemFlags';
 import {legacyListenToTopLevelEvent} from './DOMLegacyEventPluginSystem';
 import {listenToTopLevelEvent} from './DOMModernPluginEventSystem';
 
@@ -219,7 +219,12 @@ function trapReplayableEventForContainer(
   container: Container,
   listenerMap: ElementListenerMap,
 ) {
-  listenToTopLevelEvent(topLevelType, ((container: any): Element), listenerMap);
+  listenToTopLevelEvent(
+    topLevelType,
+    ((container: any): Element),
+    listenerMap,
+    PLUGIN_EVENT_SYSTEM,
+  );
 }
 
 function trapReplayableEventForDocument(
diff --git a/packages/react-dom/src/events/SimpleEventPlugin.js b/packages/react-dom/src/events/SimpleEventPlugin.js
index a2a0c9332f..f394c3dc75 100644
--- a/packages/react-dom/src/events/SimpleEventPlugin.js
+++ b/packages/react-dom/src/events/SimpleEventPlugin.js
@@ -17,6 +17,7 @@ import type {PluginModule} from 'legacy-events/PluginModuleType';
 import type {EventSystemFlags} from 'legacy-events/EventSystemFlags';
 
 import SyntheticEvent from 'legacy-events/SyntheticEvent';
+import {IS_TARGET_PHASE_ONLY} from 'legacy-events/EventSystemFlags';
 
 import * as DOMTopLevelEventTypes from './DOMTopLevelEventTypes';
 import {
@@ -38,7 +39,7 @@ import SyntheticWheelEvent from './SyntheticWheelEvent';
 import getEventCharCode from './getEventCharCode';
 import accumulateTwoPhaseListeners from './accumulateTwoPhaseListeners';
 import accumulateEventTargetListeners from './accumulateEventTargetListeners';
-import {IS_TARGET_EVENT_ONLY} from 'legacy-events/EventSystemFlags';
+
 import {enableUseEventAPI} from 'shared/ReactFeatureFlags';
 
 // Only used in DEV for exhaustiveness validation.
@@ -210,7 +211,7 @@ const SimpleEventPlugin: PluginModule<MouseEvent> = {
     if (
       enableUseEventAPI &&
       eventSystemFlags !== undefined &&
-      eventSystemFlags & IS_TARGET_EVENT_ONLY &&
+      eventSystemFlags & IS_TARGET_PHASE_ONLY &&
       targetContainer != null
     ) {
       accumulateEventTargetListeners(event, targetContainer);