Hello @devnull, just recently I came across this post: https://askubuntu.com/questions/1298690/asus-pn50-amd-ryzen-5-4500u-graphic-drivers which is why I have resigned to waiting for a regular dom0 kernel update to 5.8 or newer.
WARNING: Actually I also tried a newer kernel from the latest repository, but this left my system failing at boot and I needed quiet some time to recover it - perhaps due to my lack of experience.
Maybe a newer kernel could also fix your issues with similar hardware.