iOS build fails with fmt consteval error on Xcode 15/16 (C++20 / fmt incompatibility)

[PandorasBoxTool2024]

Description

🐛 Issue: fmt consteval compile errors on latest Xcode

Environment

• Xcode: newest version
• React Native: 80.1
• C++ standard: c++20
• Dependency: fmt (via Pods)

---

Problem

After updating to the latest Xcode version, the iOS build fails with errors inside fmt headers:

Steps to reproduce

When i try to run it with npm run ios or when i try to build direct in xcode with the older version all works fine

React Native Version

0.80.1

Affected Platforms

Build - MacOS, Runtime - iOS

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

info Fetching system and libraries information...
System:
  OS: macOS 26.5.1
  CPU: (8) arm64 Apple M2
  Memory: 141.05 MB / 8.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 18.20.8
    path: /opt/homebrew/opt/node@18/bin/node
  Yarn: Not Found
  npm:
    version: 10.8.2
    path: /opt/homebrew/opt/node@18/bin/npm
  Watchman:
    version: 2025.08.25.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/opt/ruby/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.5
      - iOS 26.5
      - macOS 26.5
      - tvOS 26.5
      - visionOS 26.5
      - watchOS 26.5
  Android SDK: Not Found
IDEs:
  Android Studio: Not Found
  Xcode:
    version: 26.5/17F42
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 19.0.2
    path: /usr/bin/javac
  Ruby:
    version: 3.4.5
    path: /opt/homebrew/opt/ruby/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 19.0.0
    wanted: 19.0.0
  react:
    installed: 19.1.0
    wanted: 19.1.0
  react-native:
    installed: 0.80.1
    wanted: 0.80.1
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: false
  newArchEnabled: false

info React Native v0.85.3 is now available (your project is running on v0.80.1).
info Changelog: https://github.com/facebook/react-native/releases/tag/v0.85.3
info Diff: https://react-native-community.github.io/upgrade-helper/?from=0.80.1&to=0.85.3
info For more info, check out "https://reactnative.dev/docs/upgrading?os=macos".

Stacktrace or Logs

error Failed to build ios project. "xcodebuild" exited with error code '65'. To debug build logs further, consider building your app with Xcode.app, by opening 'Test.xcworkspace'.

MANDATORY Reproducer

https://github.com/PandorasBoxTool2024/idontknow

Screenshots and Videos

No response

[react-native-bot]

Caution

Too old version: It looks like your issue or the example you provided uses a Too Old Version of React Native.

Due to the number of issues we receive, we're currently only accepting new issues against one of the supported versions. Please upgrade to latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If you cannot upgrade, please open your issue on StackOverflow to get further community support.

[react-native-bot]

Caution

Too old version: It looks like your issue or the example you provided uses a Too Old Version of React Native.

Due to the number of issues we receive, we're currently only accepting new issues against one of the supported versions. Please upgrade to latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If you cannot upgrade, please open your issue on StackOverflow to get further community support.