Set Camera to UI bound?

Hi, I want to make an interface similar to Citra for Android but I don’t where to start.
The final result in my mind it’s like the top screen with the viewport and the bottom part with a menu screen and a central joystick.
I tried asking to gemini but it didn’t work. For making the game running better and to learn while coding, I’d like to implement this in c++. Any suggestion?

is that an emulator?

for the buttons you can use the on screen touch input system. that already exists. but that’s for touch screens.
as for the split screen you can do this:

use a “multiplayer” split screen (non networked).
or use a texture with a scene capture for one of the screens.
the 1st one will take a bit of set up. but will be much more performant (i think).