When I’m too lazy or stupid to ‘fix’ it…
# brute force troubleshooting...
mv ~/.config ~/.configBORKED
# logout and log back in again to force plasma to recreate the folder with default settings
dolphin --split ~/.config ~/.configBORKED
# copy back half of the BORKED folder contents at a time and relog to see if issue returns
# if it does, then delete the folder again, relog, and only copy half of that previous half
# repeat until the culprit is found, then finally, copy back everything BUT that culprit bit