Comment 0 for bug 1842954

This is obviously caused by a bug in the xserver-xorg-video-amdgpu package ver: 19.0.1* which is shipped with Ubuntu 19.04 and 19.10. Upstream fix is needed.

Workaround:
sudo nano /etc/apt/sources.list, copy-paste one line which contains "main multiverse universe restricted" and change the distribution name "eon" or "disco" to "bionic" (for this line only)
So you will have a line like
deb [url] bionic multiverse main restricted universe
ctrl+o, save it

sudo update
sudo apt install xserver-xorg-core=2:1.19.6-1ubuntu4
sudo apt install xserver-xorg-video-amdgpu=18.0.1-1

sudo reboot

If everything is OK then you should keep these packages by using:
sudo apt-mark hold xserver-xorg-core=2:1.19.6-1ubuntu4
sudo apt-mark hold xserver-xorg-video-amdgpu=18.0.1-1

You can later unhold them by using the same commands with "unhold"

If a newer bionic package version comes out (fe. a security update) you should unhold the packages do an apt update and use apt policy [package name without = and version] to check the new bionic versions that you can install using my original install commands with the proper version paramter.

If something is not OK, then press E on grub menu, paste nomodeset parameter at the and of the kernel line then f10. After the kernel loading and the command line login you should just do an apt upgrade if you hadn't held the packages before.