[panpanna]

A lot of people here recommend Flutter, React and similar. But these build upon frontend technologies and use a frontend mindset you might find very difficult to get into.

If you know Java, I would instead recommend going through Googles new Kotlin courses for a week or so and see where that leads you:

https://www.udacity.com/course/kotlin-bootcamp-for-programme...

https://codelabs.developers.google.com/advanced-android-kotl...

https://codelabs.developers.google.com/codelabs/kotlin-andro...

Worst case, you have learned som kotlin which may eventually help you in your day job since kotlin is getting big in backend too.