SUMMARY
Suddenly I had many wierd problems (missing systray icons, freezes in systemsettings on specific modules, etc) with my KDE session. 

STEPS TO REPRODUCE
1. Enable night colors
2. Set up proxy (I'm using PAC) 
3. (Re)Start kded5 

OBSERVED RESULT
kded5 freezes at the stage of starting the location services. As a consequence many features are broken (missing systray icons, systemsettings also freezes/times out due inability to get response via dbus)

EXPECTED RESULT
Should finish the startup sequence, and serve the requests.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Ubuntu 22.04
KDE Plasma Version:  5.24.6
KDE Frameworks Version:  5.92.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION
I traced the problem to kded5. Kded5 freezes if proxy (PAC) is enabled at startup. It looks like it attempts to start the location service, where it freezes:
$ kded5 --replace
kcm_touchpad: Using X11 backend
Installing the delayed initialization callback.
org.kde.plasma.dataengine.geolocation: gpsd not found
"location"
It turned out enabling the night colors triggers the location services, which looks like unable to operate properly with proxy enabled.