I recently installed the unity-desktop
not knowing that it would change my login manager, and that KDE & Unity generally don't play well together. How can I restore the default KDE login manager for Kubuntu 17.04? I believe that it is SDDM, but I'm not sure.
You can try to reconfigure the sddm package with the command:
A list should appear asking for the default login manager, select sddm and the login manager should be changed.
Previous command didn't work for me. The following worked :
Source : What methods are there to restore a deleted theme? file:///usr/share/sddm//themes/breeze/Main.qml:No such file or directory