fix: Prevent stale Fabric mount updates from overriding newer Native Animated synchronous prop updates.

Author: jingjing2222

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsDefaults.kt

@@ -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.
  *
- * @generated SignedSource<<d2b14345bf627e35562530912b3aae1f>>
+ * @generated SignedSource<<a9a8ce443fa160a7494fc1c9e7baa02f>>
  */
 
 /**
@@ -153,7 +153,7 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun hideOffscreenVirtualViewsOnIOS(): Boolean = false
 
-  override fun overrideBySynchronousMountPropsAtMountingAndroid(): Boolean = false
+  override fun overrideBySynchronousMountPropsAtMountingAndroid(): Boolean = true
 
   override fun perfIssuesEnabled(): Boolean = false
 

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlagsDefaults.h

@@ -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.
  *
- * @generated SignedSource<<4a2fd61cbcdb28042f09ccb03c970674>>
+ * @generated SignedSource<<d987528598996fc7b1bf3c872f51e2ed>>
  */
 
 /**
@@ -288,7 +288,7 @@ class ReactNativeFeatureFlagsDefaults : public ReactNativeFeatureFlagsProvider {
   }
 
   bool overrideBySynchronousMountPropsAtMountingAndroid() override {
-    return false;
+    return true;
   }
 
   bool perfIssuesEnabled() override {

packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.config.js

@@ -743,7 +743,7 @@ const definitions: FeatureFlagDefinitions = {
       ossReleaseStage: 'none',
     },
     overrideBySynchronousMountPropsAtMountingAndroid: {
-      defaultValue: false,
+      defaultValue: true,
       metadata: {
         dateAdded: '2025-09-04',
         description:

packages/react-native/src/private/featureflags/ReactNativeFeatureFlags.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.
  *
- * @generated SignedSource<<aa202d346e68c3dd641d557306964ebe>>
+ * @generated SignedSource<<1dd51a152bb30c0e2073a14566c8368d>>
  * @flow strict
  * @noformat
  */
@@ -468,7 +468,7 @@ export const hideOffscreenVirtualViewsOnIOS: Getter<boolean> = createNativeFlagG
 /**
  * Override props at mounting with synchronously mounted (i.e. direct manipulation) props from Native Animated.
  */
-export const overrideBySynchronousMountPropsAtMountingAndroid: Getter<boolean> = createNativeFlagGetter('overrideBySynchronousMountPropsAtMountingAndroid', false);
+export const overrideBySynchronousMountPropsAtMountingAndroid: Getter<boolean> = createNativeFlagGetter('overrideBySynchronousMountPropsAtMountingAndroid', true);
 /**
  * Enable reporting Performance Issues (`detail.devtools.performanceIssue`). Displayed in the V2 Performance Monitor and the "Performance Issues" sub-panel in DevTools.
  */