Earlier quoted context omitted.
I had the opposite experience with Flutter personally, the problem is that Dart is a niche language with limited exposure (Flutter is basically the only big project in Dart realistically) and it's also a new project as well, it makes a bad combination.
Could you describe your experience more in details? What exactly didn't work out? I would like to know to understand whether it makes sense for me to invest my time in Flutter/Dart instead of a more mature solution like React Native.
I don't know what you are trying to build on mobile but I'd definitely learn Flutter instead of RN, which I have. Others here have said you should just go full native instead, and they're probably right.