Plasma 6: Can't delete 3 sddm login splash screens


the latest update brought Plasma 6 to my system. Apart from all the other problems that were already reported by many people, I do have a minor problem that nonetheless is driving me crazy: once upon a time I installed some login splash themes for sddm, which I can not delete any more. These themes were installed using “systemsettings”, not by apt, and they show up in “systemsettings”, but I can click onto the trash bin, then “apply”, and “systemsettings” tells me that the packages have been deleted, but they never disappear from systemsettings, not even after a complete reboot.

I manually search the hard drive for any occurrences of files that are related to those themes and then I deleted those files, but they still appear in systemsettings.

I am out of ideas of how to get rid of those packages showing up in systemsettings.

Does anyone else have any idea?