I had similar issues with a Ryzen 5 4500U. Without AMDGPU in Xorg I had no HDMI/DisplayPort output and xrandr only showed a single output called “default”.
Here’s what worked for me in Qubes-4.1-20200830:
In dom0, install xorg-x11-drv-amdgpu and kernel-latest.
Reboot.
This booted into Linux 5.7.12, which has KMS support, allowing the AMDGPU driver to load in Xorg. The older kernel from the kernel package does not seem to support KMS on AMDGPU. The most obvious evidence that KMS was enabled was that the boot showed graphics (Qubes logo with progress bar below) rather than just text.
But since 4.1 is too unstable for me atm i wonder if i can compile, maybe older stable versions, for fedora-25 dom0? I think all i am missing is the xf86-video-amdgpu from xorg? Do i need to take a look into the qubes builder process/documentation or is there an easier way?
I am familiar with compiling packages from source.
The xorg-x11-drv-amdgpu package is available on Fedora 25, but it’s from 2017. kernel-latest on Qubes 4.0 is at 5.6.16. I have my doubts, but it may be worth giving those packages a try.
Just installed xorg-x11-drv-amdgpu and for now it runs fine. Didn’t even have to switch to kernel-latest.
$ grep EE /var/log/Xorg.0.log
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[ 42.328] (EE) AMDGPU(0): glamor detected, failed to initialize EGL.
[ 42.349] (EE) AIGLX: reverting to software rendering
Since whole dom0/fedora 25 is outdated i don’t mind having amdgpu drivers from 2017.
I’ll take a look into configuring and testing suspend but this is way better than using vesa drivers.