Flutter has a larger number of "star" on Github. It also has more issues and more pull requests.
React Native has 3x more followers on Reddit.
So I guess it depends on your definition of community.
Flutter is only in beta for desktop and web.
And it's emulated UI, not true native UI.
RN is ready now and today for all platforms, including Window via react-native-windows.
Microsoft is choosing React, I wouldn't go w/ Flutter.
Why would you choose a Google only language and framework... unless you like rewriting code when it dies.
Also, w/ React you can use TypeScript or JS, you don't have to learn a new language.
From my perspective, it looks like Google pays a lot of money for these tech articles and stars, it's not a really good way to look at things. There's always a Flutter campaign going on.
As much as I hate that google kills stuff often, the above comment is missing the fact that facebook also kills stuff often, they just never had any adoption in the first place so you don't notice
But React is more open source and flexible. Microsoft has embraced React and RN via their react-native-windows project, they are currently rewriting it from C# to C++, so it must be important.
They use it for Skype and other products.
Google isn't built on Flutter, not the important parts. Facebook has been building their stuff w/ React. They have over 10,000 components, I doubt they'll abandon it.
Even if they do, React is much more flexible and open, it doesn't have a compiler or language tied to it either. If Google drops Flutter, you're fucked.