Created attachment 142071 [details]
Log of running systemsettings5 in the terminal.

SUMMARY
I use openSUSE Argon which uses the KDE repos on top of the main repos offered in Leap. The current version of Plasma (5.22.90), has an error in System Settings, where the Font Management KCM (kcm_fontinst.so) can't be loaded. System Settings reports 'KPluginFactory could not load the plugin: /usr/lib64/qt5/plugins/kcms/kcm_fontinst.so . However, the file in question IS PRESENT in that location. I know there is a similar bug in the Wayland session reported here: https://bugs.kde.org/show_bug.cgi?id=439375, but I'm encountering this problem in X11.

STEPS TO REPRODUCE
1. Open System Settings 
2. Go to Appearance -> Font Management
3. See error message

OBSERVED RESULT
System Settings reports 'KPluginFactory could not load the plugin: /usr/lib64/qt5/plugins/kcms/kcm_fontinst.so .

EXPECTED RESULT
The Font Management KCM loads normally, to allow font installation.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Leap 15.3
KDE Plasma Version: 5.22.90
KDE Frameworks Version: 5.86.0
Qt Version: 5.15.2
Kernel Version: 5.3.18-57-default (64-bit)
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-3320M CPU @ 2.60GHz
Memory: 7.6 GiB of RAM
Graphics Processor: Mesa DRI Intel® HD Graphics 4000

ADDITIONAL INFORMATION
I've also attached a screenshot and the log of System Settings.