First, make sure that your the only entry in your
/etc/apt/sources.list file is the following:
deb https://repo.pureos.net/pureos/ green main
Second, make sure that all your packages are up-to-date, using
sudo apt upate && sudo apt full-upgrade.
Third, at the login screen, try clicking on the gear below the password box, and choose, “GNOME on Xorg” (assuming you haven’t done this before), log in, and then see if you still have that problem.