I don’t know how it works in RetroArch, with Delta/Ignited you can change the skin which also manages the size and position of the screens. I even designed custom skins to play full screen with no controls with Zelda since you don’t need the abxy and arrow buttons to play.

Mypizzaboy is the best android emulator tbh

If retroarch is too much you can try Lemuroid. Lemuroid is a much simpler emulation app with a more straightforward GUI. It doesn’t come anywhere near the features or number of cores of retroarch but it supports most common retro systems.

If you’re only interested in a few consoles you could try dedicated emulators.

You can change scaling in options gear > user interface > appearance > menu scale factor