This post is a 15,2 version of https://forums.op the problem does NOT occur under Wayland,ensuse.org/showthread.php/560079-Repeated-Kded5-crashes-since-Sept-20-update?highlight=kwin.
After experiencing this problem, which occurs only with Plasma (X11), I found several occurrences that referred to Kwin and “window decorations”. After reverting to “Breeze” in theme and decorations, problem ceased.
FWIW, the problem does NOT occur under Wayland (although many other problems were observed).