i saw a video about this: https://www.youtube.com/watch?v=bP_8EYQ-2RA
i think the best good card it terms of compatibility would be the one think penguin sell:
https://www.thinkpenguin.com/gnu-linux/geforce-8400gs-1gb-pci-express-20-video-card-gnulinux-full-low-profile-brackets but it might not be as portable you can also check h-node for a list of freedom compatible gpu's: https://h-node.org/videocards/catalogue/en
