We don't need these arguments anymore. In fact I think the key is to force the server to boot with the IGPU (in the bios) and to exclude the Nvidia GPU in the /etc/modprobe.d/nvidia.conf file with the following lines:https://www.youtube.com/watch?v=zIMZrwF60qM
echo "softdep nouveau pre: vfio-pci" >> /etc/modprobe.d/nvidia.conf
echo "softdep nvidia pre: vfio-pci" >> /etc/modprobe.d/nvidia.conf
echo "softdep nvidia* pre: vfio-pci" >> /etc/modprobe.d/nvidia.conf
So I have my Windows and Linux VMs booting with the Nvidia GPU in Q35/OVMF
And very very important, don't forget to put in the bios the video mode on "IGPU" to force the host system not to use the Nvidia GPU. If this is not done, error 43 guarantee!