Sep 7, 2018, 10:53 AM by luigi.toscano@tiscali.it:
I suspect (given the lack also of kwin-x11) that you installed disabling the packages marked as "Recommends", and most of the issues are coming from this.
Check for example the Recommends section of the plasma-desktop package:
https://packages.debian.org/buster/plasma-desktop <https://packages.debian.org/buster/plasma-desktop>
Installing systemsettings package resolved the issue. Kind of strange that this package is not a part of kde-standard, I use it often.