So I installed with the spice server as hardware, without any passthrough.
Then I remove the spice server and the QXL video card and added the passthrough.
Windows is starting on my screen, I can enter it. I tried to install the drivers but I can’t get it working. The 970 GTX is recognized as code 43 . So I’m going to follow the tutorial previously linked.
But so I can confirm that it’s normal I guess that the windows installation doesn’t work well with gpu passthrough right away.