I agree with Gforcez, recently I've started developing my frontend part of a mobile app in Flutter framework and I must say it is delightful and very suggestible making the code writing under a logic tree of objects.
A plus is that this is a cross-platform framework written in Dart language from Google, and I think it is one of the next biggest languages that will come into companies.

But yes, this is just for the frontend experience, but for backend I suggest to go for a Java/C#/Python written in server. I use always a C# server for any type of app by configuring it to run on linux under a docker.

However I have to say this framework is the best for an app that doesn't requires complex algorithms that requires optimisation and performance, like a mobile antivirus, memory cleaner, and other stuffs that works with the OS of the mobile. But if your app is like an Instagram, Facebook, Messenger, and other apps that keeps the bussiness logic in the server and not on the client, then I suggest to make an app in a native way, with Android Studio for Android and Swift/Objective-C for IOS.