Given the discussion of the recent ReactXP thread, I'm guessing most people don't realize you can do this today. React Native supports macOS [1] and UWP [2].
Edit: There's even some early work on Ubuntu support [3].
[1] https://github.com/ptmt/react-native-macos
[2] https://github.com/Microsoft/react-native-windows
[3] https://github.com/CanonicalLtd/react-native/blob/ubuntu/REA...