Okay, so I think all this happened because I changed the KDE theme to Breeze Dark but selected “Desktop and window layout,” which has a warning about what it changes, such as panels, docks, etc.
I didn’t check that box on the new user account when applying the same Breeze Dark theme, and it seems to work for that account at that moment.
I restarted my laptop to see if it would log in successfully, but then that user account also had the same exact problem as before.
I’m wondering if this is just a KDE issue now.
EDIT: The default openSUSE KDE Theme that’s applied by default works fine and has no issues.