Ive tried booting from different kernels in the grub menu, reinstalling sddm, reinstalling graphics driver, and even trying to bypass sddm alltogether, all of which without any of it making a difference for the issue. The only fix i find is plugging in one of the displayports into the motherboard, but this is no fun to always do and not even a consistent solution.
how do you have updated your system as the best way in case hardware vendor drivers are involved is to disable them during the update process and use the opensource ones. After updating the system enable them again via:
sudo apt update && upgrade
sudo ubuntu-drivers autoinstall
after installation of the recommended drivers
sudo reboot
However, I have to admit that you maybe already tried this but I have seen similar user reports (different kernel(s) + driver(s)).
Not necessarily but irrelevant because AMD graphics drivers are open-source and already included. But even if relevant the command is outdated. Now it’s just
