Modal `formSheet` backdrop fade animation missing on first modal creating unsmooth experience.

Description

When presenting a <Modal> with presentationStyle="formSheet" and animationType="slide", the backdrop dimming overlay does not fade in on physical iOS devices. Instead, the dimming appears instantly without animation when the first modal opens, results in a jarring, unsmooth appearance when opening modals.

Native apps do not have this problem, so it is unfortunate that all react-native apps suffer from this visual downgrade.

The modal sheet itself slides up correctly, only the backdrop transition is broken.

Notably:

• The second modal's backdrop animates correctly
• Modal dismissal backdrop fade-out always works correctly
• The iOS Simulator works correctly - the bug only appears on physical hardware

This was originally reported against react-native-screens (https://github.com/software-mansion/react-native-screens/issues/2977), but the issue reproduces with React Native's built-in <Modal>.

Steps to reproduce

1. Create a fresh React Native 0.84 project
2. Use the reproduction code below
3. Build and run on a physical iOS device
4. Tap "Open Modal 1" — observe the backdrop appears instantly (no fade)
5. Tap "Open Modal 2" — observe the backdrop fades in correctly this time
6. Close both modals and repeat — the first modal's backdrop never animates

React Native Version

0.84.0

Affected Platforms

Runtime - iOS

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

System:
  OS: macOS 15.6
  CPU: (14) arm64 Apple M4 Pro
  Memory: 3.64 GB / 64.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.13.0
    path: /Users/kris/.nvm/versions/node/v22.13.0/bin/node
  Yarn:
    version: 1.22.22
    path: /Users/kris/.nvm/versions/node/v22.13.0/bin/yarn
  npm:
    version: 10.9.2
    path: /Users/kris/.nvm/versions/node/v22.13.0/bin/npm
  Watchman:
    version: 2024.12.02.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/kris/.rbenv/shims/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.4
      - iOS 18.4
      - macOS 15.4
      - tvOS 18.4
      - visionOS 2.4
      - watchOS 11.4
  Android SDK: Not Found
IDEs:
  Android Studio: 2024.2 AI-242.23726.103.2422.12816248
  Xcode:
    version: 16.3/16E140
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 3.1.6
    path: /Users/kris/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.84.1
    wanted: 0.84.1
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

None

MANDATORY Reproducer

https://snack.expo.dev/@supermelle/modal-native

Screenshots and Videos

In this video it it shown, how the animation on the first backdrop is missing, and also how it is working on the second modal.

https://github.com/user-attachments/assets/ba417a57-1b14-44b2-a197-59d5f3ffb3fa

从必需的 Snack 复现开始，并在实体 iOS 设备上运行它，比较使用 animationType="slide" 的第一个和第二个 formSheet 模态框。跟踪内置 React Native Modal 的呈现路径，检查 backdrop 过渡。完成的标准是：第一个模态框的 backdrop 在实体硬件上平滑淡入，同时关闭操作和后续模态框仍然正确。