Adityavardhan Singh I would suggest you to take up Java because C++ is kind of semi OOP because you can run a program without having a class.
Whereas Java is fully OOP, I'm saying this because only primitive data types did not have classes but then you have wrapper classes for them.
I don't want to get into the details and since you want to get into app development, Java is one of the best languages for that.
it depends for you. If I have choose these two. I take definitely Java. It's more simple than Python. (if you have basics c++ background). My pinion Sololearn java course is far more upfront than Python cource. Seriously Python is them how wanted make AI like neural networks or data analysis. For that purpose it works fine. But finished only any Sololearn course you don't have skills able make that kind things. You must practice coding over and over again.. Sad but true. Anyway take Java! :)