What language to use to build (cross-platform) app

Question

I have experience in making simple programs in python that take simple inputs and outputs and some really small games in pygame, but I want to make a bit more robust app with gui, which will work with local databases or even connect to server for data. I'd also like to make it as cross-platform as possible.
Question is: Should I use python or should I try different languages and what modules/libraries to use?

Answer 1

Tomáš David
Can you explain what the app is,more clearly?
I feel the description of "cross platform gui app" is too vague.
Example: a word generator, a 2d game. A MMO.

Answer 2

I've been using Flutter lately and it's been great for Android/iOS development. I think it works for mobile games too, but I can't say for sure since I haven't tried that yet.

Answer 3

Manual
There are two of them: one is some sort of game, but i don't have the exact idea yet, the other one is app where you choose things you want to take o with you for tour and it will take data about those things from local/web database and say which things to pit together to distribute them evenly among all people