I would say that your best bet would be to learn React Native. It’s an excellent option for mobile apps and you can reuse what you learn for a lot of other things as well. It’s super popular so you should find no shortage of resources if you get stuck.

Another option is Flutter. I personally don’t like it too much unless I also intend to target desktop (and even then I’d probably use something else) but it’s fairly popular as well so you should be able to find plenty of learning resources.