I had the same issue on popos Cosmic alpha and I couldn't login to the desktop, kept getting error messages since it probably didnt finish upgrading before I powered down manually, so I had to hit
Ctrl + Alt + F2
Logged with usename and password into terminal
Some terminal commands that fixed it for me (not necessarily in this order)
sudo dpgk --configure -a
sudo apt update
sudo apt full-upgrade
sudo apt autoremove
sudo apt autoclean
I'm running Cosmic and have been having issues with updates through popshop. Running updates manually through terminal has been more reliable, otherwise i gotta run sudo apt full-upgrade every now and then to fix whatever broke with popshop upgrades.
Good luck.
right or left edge for me, gotta maximize that vertical space