Why do you need Nvidia in dom0?
There is no graphics hardware accelerations available for qubes from GPU in dom0.
So GPU in dom0 only used to output the image received from qubes. GPU won’t render anything inside qubes, the CPU will be used for rendering.
But you can passthrough your Nvidia GPU to some qube and use it there for 3D-accelerated tasks:
The Intel GPU will be more than enough for dom0 tasks. So you can use your Nvidia GPU inside some qube instead.
But if you still want to use Nvidia in dom0 then you can try to check your BIOS settings, try to find some option to set Primary GPU or maybe disable integrated GPU.
You want help with installing Qubes OS 4.1.2?
I don’t think it’s a good idea, the Qubes OS 4.1.2 won’t be supported anymore in June: