That didn’t do the trick… During the installation the opensuse branding was removed and upstream installed. during the next reboot KDM defaulted to the very classic KDM manager. I checked kdmrc and the settings appear correct, even manually editing the theme line doesn’t help
Go to YaST, System, /etc/sysconfig editor, Desktop, Display Manager, DISPLAYMANAGER_KDM_THEME= and set it to whatever you want. That was the only way I could get it to change. You’ll need to restart KDM after changing the value. Mine is set to oxygen. Hope that helps!