Thanks for your efforts. This is very strange. As root or a local user, as we tried and reported, the kmdr-editor will freeze the machine while starting. As a NIS user, kmdr-editor and kmdr-executor work fine. I even tried to copy the ~/.kde from a NIS user to the local user and correct the user rights, but this did not help. The machine we use is a machine which we migrated from Leap 15.3 to Leap 15.4, but this should not make a difference.