It turns out that QXL is essential. I must have checked incorrectly whether it works after removing it. Without QXL, there is no image from the GPU, just a black screen. After adding it back, the graphics card outputs an image (the monitor name is now displayed instead of vDisplay). I’m not entirely sure what’s going on here, but I’m satisfied with the result.
Thanks @perrine for the script and suggestions.
I finally got around to testing again with a new VM and with QXL… Sadly, I cannot (simply) use BIOS instead of UEFI, because my existing Windows installation was done on a bare metal M.2 drive from a UEFI system. While I could attempt to convert the disk partition style, I’m not willing to risk potential data loss.
The only thing left to try is a fresh Windows install relying on virtualized storage, but that would only be for more testing.
It seems I’ll again hold off on GPU passthrough until getting another M.2 drive for a fresh Windows install.
I am having the exact same issue now. It has been working fine for months - but today the screen is just garbled.
Anyone ever been able to fix the issue with the garbled screen?
Hello, I would like to ask on how are the iommu grouped when 2 gpus are installed (x570-f) and if it would be possible to passthrough each to a different VM?
I can confirm the X570-F Strix has good IOMMU group separation and both my GPUs are in separate groups. Pass-through would be difficult otherwise.
If you’d like more info I’m happy to help, but it might pay to make a new topic. 
I’ve made a topic and I would be glad for your help and insight on this.