> One thing I want to figure out (because I don't have a dedicated Windows gaming desktop), and the documentation on the internet seems sparse: it is my understanding that if I want to use PCIe passthrough with Windows VM, these GPUs cannot be available to the host machine at all, or technically it can, but I need to do some scripting to make sure the NVIDIA driver doesn't own these PCIe lanes before open Windows VM and re-enable it after shutdown?

The latter statement is correct. The GPU can be attached to the host but it has to be detached from the host before the VM starts using it. You may also need to get a dump of the GPU ROM and configure your VM to load it at start up.

Regarding the script, mine resembles [0]. You need to remove the NVIDIA drivers and then attach the card to VFIO. And then the opposite afterwards. You may also need to image your GPU ROM [1]

[0]: https://techblog.jeppson.org/2019/10/primary-vga-passthrough...

[1]: https://clayfreeman.github.io/gpu-passthrough/#imaging-the-g...