Hi, I assume you're using testing. Unfortunately, Plasma is broken in testing at the moment if you have upgraded libkdecorations2-5v5 to 5.23. Could you check that ?
If this is the case, I wrote about a possible solution here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=996726#10 -- Med vänliga hälsningar Patrick Franz
