(In reply to Leon from comment #19)
> By the way, since I have a x470 mb, it cannot be related to PCI express 4.0.
> It's also not related to dual displays, since I'm running just one.

Not necessarily. Some x370 and x470 motherboards erroneously reported PCIE 4.0
support in earlier BIOS (AGESA) updates. You might want to update to the latest
available bios, if that is the case with your board.

Although, since you are using 5.3.1 I don't think the bug has been fixed in
mainline 5.3 yet. You might want to use amd-staging-drm-next, or wait for
4.1-rc1.