I realized this & looked the cmd history up. I absolutely did do it (and I can absolutely remember it). I did every step in this tutorial: Nvidia proprietary driver installation and a few hours ago it worked once.
However, I did this tutorial again now. But even if lspci now shows that nvidia driver is there (which I am absolutely sure it did a few days ago too), i still get the same errors on every try.
I thought this tutorial may be good because it mentions some other additional commands: How to Install an Nvidia Driver | Qubes OS . However, once I did ./nvidia-xconfig & reboot my system now I get this error (even when using nomodeset):
“Failed to start lightdm.service - Light Display Manager”.