there's a guy on YouTube who's implemented his own imaginary virtual retro computer and is programming it with LLM assistance. I don't find that interesting to watch, so I don't know how successful it's been, but I assume it's fine.
I've asked Claude for help with 6502 assembly for C64, and it's seemingly quite competent. The training probably doesn't focus on it, but the models are so big and the retro machines so small and simple, they can just do it.