What are your system specs and which Zorin? Core or Lite?
On the lock screen, click the little gear button and see if switching to Wayland desktop helps.
If not, press ctrl+alt+Fn3 (maybe anywhere from Fn1-6 for you) to get a terminal. Then, for:
Core: sudo apt --reinstall install gdm3
Lite: sudo apt --reinstall install lightdm
See if that fixes it.
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