How to install proprietary gpu driver?

[Ir Jean-Charles de Longueville]

Hi,
I'm installing my second desktop with Qubes-OS 3.2.
The first one has a NVidia gpu and the other an AMD one.
Both are connected to 4K display trough display port.
And both have problem with display.
It looks like nor nouveau nor radeon can properly manage 4K displays :(
I read a lot of docs (twice) and googled quite a bit but did not find
official doc nor any blog on this topic:

How to install proprietary gpu driver in Qubes-OS ? (nVidia or AMD)

Thanks for reading,
Jean-Charles