On the current version (and some previous versions) of PopOS if you are running on a laptop (I have an Oryx for example) and you try to use SDDM login manager you may find yourself with a black screen instead of a login screen after reboot. Pressing ctrl-alt-f2 to get to a shell you can easily fix the problem by adding a single xrandr command to the sddm setup script. Simply add this command to /usr/share/sddm/scripts/Xsetup
Then reboot, or restart the login manager and you should be able to see your sddm login screen. If the screen is still blank, as it was on the late 2021 Oryx xrandr may not be able to autodetect your resolution. You can get around it by running
on a command line, checking the display being used (in my case it was eDP-1-1) and manually setting the resolution in the /usr/share/sddm/scripts/Xsetup script with this command instead:
xrandr –output eDP-1-1 –mode 1920×1080
Your resolution and output name may vary but using ‘xrandr -q’ while booted into X (through gdm for example) will give you the info you need.
If you are presented with the software keyboard on load you can disable it by editing /etc/sddm.conf and adding the line
(yes, that is an equals with nothing after it).