Question regarding where to aim my focus

Question

I have an idea for an app/game which I'd like to be multiplatform (browser, android, ios) and involves a high level of user to user interaction. What should I know and be learning to create this project? I have been learning the JavaScript language along with HTML and CSS.

Answer 1

Since u are aiming for developing an app,which is multiplatform:
I suggest learning FLUTTER...

Answer 2

Two of the biggest game engines (Unreal and Unity) use C++ and C# respectively, but there are engines for almost every language. In my opinion, C# is better for this kind of thing, but choose the one that suits you better.

Answer 3

Browser game dev enough for the start