Hello. Yes, it just works… passthrough work on gnu/linux standalone qubes, and you can plug an external monitor too. Windows is another thing, the GPU is detected, and works, but external monitors don’t get any output, so you can run heavy tasks on windows but without external monitors limit use cases (like gaming), you can try proton via steam to game on gnu/linux VMs.
to get it working read the following article: https://forum.qubes-os.org/t/create-a-gaming-hvm/19000