The mobile world is dominated by Apple's iOS and Google's Android. Since iOS is not open source the only avenue that is left to explore is Android. And, surprisingly, there are options available that actually work very well. Which one you choose depends on

Self-hosting can easily become very time consuming. Container technology doesn't solve all the problems. Yes, it's getting easier to deploy web applications and services, but you still have to update them regularly, set up a backup/restore mechanism, ensure that database migrations don't break