External Graphics card for Laptop

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

EDIT:
just remember to check that your adaptor will work with libre drivers as-well

also it might not be that much more money to buy a x200
i have one and 0ad runs quite well on it

The GPUs with best performance running free software are Kepler. I can share my benchmarks, if you don't ignore them. Yes, I tested x60 too.

Nouveau's kepler reclocking it is experimental, but works wonderful.
Another option is Intel Iris Pro.

x200 it is not much more powerful.

It may not be doable and even if it is, it's probably not worth doing.

Why it may not be doable: Few new Laptops have an Express Card to rig an Adaptor and hackery with the Mini Pcie Slot that the Wifi Card uses is whitelisted thanks to the infinite wisdom of the FCC.

Why it may not be worth doing: Older laptops that don't have the Whitelist or are Core/Libre Boot compatible have older CPUs that bottleneck the GPU, The GPU is bottlenecked by PCIe x1 anyway, even if you still want to do it and have a non-free Bios, you'll have to go through the trouble of ripping your Bios and then looking for a whitelist flag in that binary blob and turn it off and then flash it. You're also making your system less portable though it would be nice for laptops that have M.2 where you could rig that into a GPU Dock for gaming at home. (Preferably games with free engines :D)