Both Flutter and React are Amazing Frameworks and there is a huge demand as well as cutthroat Competition amongst each other.
If we go about the performance then you should go for flutter as it has its own numerous customized widgets, compiled with ARM which makes it fast, and on the other hand, react native has the javascript code also it doesn’t have the native liberties which makes it less proficient.
Also read :-What is a Motherboard of a Mobile and How does it Work?