I’m looking up for communities or scenes whose purpose is making games that you play from bootup. Not necessarily boot sector games (stuff that has to fit in 512 bytes), but things that would behave much like cartridges in old consoles, where the hardware boots straight into the game.

Put another way, games that “are the OS”, either for x86 or ARM. My search engine-fu didn’t manage to find anything other than boot sector games and several Batocera guides.