[Strict TS API] NativeSyntheticEvent doesn't match BaseSyntheticEvent

Description

My team uses unified codebase that share web and native code, so that is why a BaseSyntheticEvent event was used here.

import type {BaseSyntheticEvent} from 'react';

<TextInput onSubmitEditing={
  (event: BaseSyntheticEvent) => {
        event.bubbles; // boolean | undefined 
         // error: BaseSyntheticEvent require `boolean` only type
  }} 
/>

this issue doesn't not exist in prev. RN versions

Steps to reproduce

see above

React Native Version

0.87.0

Affected Platforms

Runtime - Android, Runtime - iOS

Output of npx @react-native-community/cli info

System:
  OS: macOS 26.5
  CPU: (11) arm64 Apple M3 Pro
  Memory: 1.27 GB / 36.00 GB
  Shell:
    version: 4.0.1
    path: /opt/homebrew/bin/fish
Binaries:
  Node:
    version: 24.13.1
    path: /usr/local/bin/node
  Yarn:
    version: 3.6.4
    path: /opt/homebrew/bin/yarn
  npm:
    version: 11.8.0
    path: /usr/local/bin/npm
  Watchman:
    version: 2025.09.01.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/xdxd/.rbenv/shims/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.2
      - iOS 26.2
      - macOS 26.2
      - tvOS 26.2
      - visionOS 26.2
      - watchOS 26.2
  Android SDK:
    API Levels:
      - "34"
      - "35"
      - "36"
    Build Tools:
      - 33.0.1
      - 34.0.0
      - 35.0.0
      - 36.0.0
      - 37.0.0
    System Images:
      - android-34 | Android TV ARM 64 v8a
      - android-34 | Google TV ARM 64 v8a
      - android-35 | Google APIs ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
      - android-36 | Android TV ARM 64 v8a
      - android-36 | Google TV ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2026.1 AI-261.23567.138.2611.15646644
  Xcode:
    version: 26.2/17C52
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /Users/xdxd/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.2.0
    wanted: 20.2.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.87.0
    wanted: 0.87.0
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

error TS2322: Type '(event: BaseSyntheticEvent) => void' is not assignable to type '(e: Readonly<{ bubbles: boolean | undefined; cancelable: boolean; currentTarget: number | ReactNativeElement; defaultPrevented: boolean; dispatchConfig: Readonly<{ registrationName: string; }>; ... 10 more ...; type: string; }>) => unknown'.
  Types of parameters 'event' and 'e' are incompatible.
    Type 'Readonly<{ bubbles: boolean | undefined; cancelable: boolean; currentTarget: number | ReactNativeElement; defaultPrevented: boolean; dispatchConfig: Readonly<{ registrationName: string; }>; ... 10 more ...; type: string; }>' is not assignable to type 'BaseSyntheticEvent<object, any, any>'.
      Types of property 'bubbles' are incompatible.
        Type 'boolean | undefined' is not assignable to type 'boolean'.
          Type 'undefined' is not assignable to type 'boolean'.

27       <TextInput onSubmitEditing={(event: BaseSyntheticEvent) => {

MANDATORY Reproducer

https://github.com/retyui/repo_with_virus_to_steal_corporate_data_so_you_get_fired_and_spend_the_rest_of_your_life_in_prison

Screenshots and Videos

...

Comienza con el tipo TextInput onSubmitEditing y la definición de NativeSyntheticEvent utilizada por React Native 0.87. Reproduce la asignación estricta de TypeScript del issue y compárala después con la tipificación de BaseSyntheticEvent de React. Se considera terminado cuando el handler indicado es compatible sin debilitar los tipos de evento relevantes, y existe una comprobación de regresión para el ejemplo mostrado.