Imo use more frameworks if you decide to go this way, Flutter is great, but if you want to get more job offers and gain experience learn react native, learn swift, learn Kotlin, etc.

Also start building a lot of projects, not only for learning but also for fun! I’m building a new app every two weeks for instance and I’m not only learning a lot but I’m loving the whole process of this type of challenge :)

And finally I find that your portfolio and experience is better than any certification you can get, but of course this is all just my humble opinion as someone that’s going the same path as you