in 2020,I found a code, can pass primary GPU to VM (R5 2600X, no iGPU)

I can't find the code again in this forum.

Now I still can passthrough the primary GPU tu a VM (win7), but, when I shutdown, passthrough to another VM (unbuntu or win10), it dead. but you can goback to the VM whitch you first passthrough, it's work well.

could anybody can tell me where it is?

update:

When I change the OS, I have to reboot the UNRAID.

which means you can passthrough primary GPU to any VM at the frist boot up, also you can reboot this VM or restart this VM for many times, but you can't change the VM.