The Mac Pro still has auxiliary power connectors, so you could theoretically install a GPU in it, just not the highest end ones. No drivers so you can't really do anything with them. I do suppose Nvidia could maybe do CUDA drivers for a card, but would Apple even allow it?
@paul I still think apple is working on their own gpu card, there were rumors about it. it just wasn't ready. the whole mac pro wasn't ready cause it’s not bringing much to table you can't just get with a studio and good thunderbolt 4 station for less. I really am just gonna wait for m3 for both 3nm and to see what they do with more time. if by then they still haven't given me a reason to care about pro, i'll get m3 studio.