SUMMARY
Quite specific, but maybe symptomatic of something else.
On login, my gpg wallet password is prompted as it should. The background is dimmed, darkened, thanks to the option that I checked in the Effect preferences (dim screen for administrator mode). But after the password was successfully given and the dialog has disappeared, the screen remains dimmed -- forever.


STEPS TO REPRODUCE
1. enable "dim screen for administrator mode"
2. have your kwallet be a gpg wallet (password will then be prompted on login invariably)
3. logout, login

It doesn't happen all the time... But it happens often. And it isn't new, I've seen it for 4 months (when I started using a gpg login wallet)

WORKAROUND
Changing the theme, like switching to breeze dark or to breeze, forces the screen to recover from the dimming.

EXPECTED RESULT
Screen should stop being dimmed after admin dialog has exited.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION