Okay, well that got me a new error.
No filter class matching [sriov]
Requested device sriov not found!
To add some detail: I'm adding the VF as a second graphics card, while leaving VNC as the primary one. This is done so I can still access the machine.
I'm certain the plugin and the virtualization work with my 12th gen. As in Windows, with the same type of setup (VNC as 1st + VF as 2nd), it works no problem.