If you have the money, make everything native, but until then I can build a Flutter app that works on 6+ platforms for the price of one, which is a real competitive advantage for a solo developer running a startup.
One thing I learned though... if you say are going to deploy on say, Android, you are not getting away from its dev toolchain and API if you want to do anything non-pedestrian. Same for iOS and possibly Windows.
So you often end up really having to learn N+1 platforms.
So you often end up really having to learn N+1 platforms.