I'm neither flutter nor react native developer just native mobile dev but evaluating both techs so don't have stake in the game right now. Just showing to other so they can make their own judgement:

Flutter monthly pulse: https://github.com/flutter/flutter/pulse/monthly "Excluding merges, 83 authors have pushed 451 commits to master and 461 commits to all branches" but:

1st engine-flutter-autoroll (bot with revisions autoroll): 185 commits

2nd zanderso (google employee): 25 commits

3rd ValentilVignal (contributor): 14 commits

in top 15 contributors for flutter you have also other bots such as: fluttergithubbot, auto-submit[bot], flutter-pub-roller-bot, dependabot[bot]

React Native monthly pulse: https://github.com/facebook/react-native/pulse/monthly "Excluding merges, 84 authors have pushed 437 commits to main and 575 commits to all branches"

1st cipolleschi (meta employee): 92 commits

2nd cortinico (meta employee): 83 commits

3rd NickGerleman (contributor): 45 commits

no bots in top 15 contributors

Also keep in mind React Native is based on React repo project. On top of that you have a lot of work by community in:

- expo https://github.com/expo/expo

- react native reanimated https://github.com/software-mansion/react-native-reanimated

- react navigation https://github.com/react-navigation/react-navigation

- react native skia https://github.com/Shopify/react-native-skia

All of those packages are highly maintained and are pretty used in all RN projects and considered standard.