Ok, apparently I managed to recover. But I don't understand anything about what happened.
I entered safe mode, activated the internet and used the command:
sudo apt install --reinstall fonts-zorin-os-core zorin-desktop-session zorin-os-desktop
That I took from this thread: Unable to boot after removing libreoffice-gtk3
I have no idea why this worked. Apparently when I did all those customizations, something went wrong.
I'm just a little worried that I've broken something in the system from the tests I've done trying to fix the problem, but apparently everything is fine...