Parent is talking about the Compute Module 4, which can plug into (among other things) a first party IO board that has a PCIe 1x slot. With a simple hardware mod (cut the slot connector, cut the GPU, use a riser, etc etc), any GPU can physically fit. He's only gotten one to work so far though, an ancient ATI card. Lots of fun YouTube videos and GitHub issues about this if you search parent's name or look at links in his profile.
