You may be interested in the work of Ali Gholami Rudi. Scroll down to the "framebuffer" section: https://litcave.rudi.ir https://litcave.rudi.ir Apart from thi

You may be interested in the work of Ali Gholami Rudi. Scroll down to the "framebuffer" section: https://litcave.rudi.ir https://litcave.rudi.ir Apart from things like writing his own C compiler and typesetting systems, Rudi implemented several GUI programs that work on Linux without Xorg or Wayland. He claims there on his site he doesn't even use Xorg any more.