John Akhilomen

Since you're new, I'd recommend Javascript and Python. With Javascript, just learn React and Node. And with Python, learn Django. With JavaScript, Node, React, Python, and Django; you can accomplish quite a lot for both frontend and backend.

Since it's a banking app, I'd advice you go with Python for the backend because of the data analysis you'd be doing in your app. I see you doing some data analysis since it's a banking app. Python is a powerful language for data analysis. And for web, yes I'd advice Node with React, and for mobile, Node with a combination of Kotlin and Swift. Don't even try going hybrid for this kind of application. It's best going native.

I'd recommend React. This is because React is very easy to learn. Furthermore, you get to code your dynamic UI components like classes and objects which will make them reusable all through your project. I find that as being one of the best features React has. Also, you get speedy development with React due to its simplistic syntax and the sharing of data among components through props. Also it's backed by Facebook and the framework is easy to integrate with other applications.

I'd have recommended MongoDB, but since you're considering Security, then PostgreSQL it is. PostgreSQL is also easy to use, stable, good documentation, and huge support community out there. PostgreSQL also handles concurrency well..