Related, check out raylib, the rendering/game engine made by the same author!
I’ve used Raylib and raygui on a few RPi based projects and recommend it. It’s a really simple, intuitive way to get an OpenGL-based UI running. Good alternative to web-based UIs because it has similar simplicity but runs on devices with lower specs. I built this pinball machine with raylib: https://youtu.be/iiBn7FVzlcc