SUMMARY
The font size on KDE Plasma desktop is shrunk to font size 6 which is barely readable and when entering into Plasma Desktop Setting for Font management to adjust both the force DPI and font size for all fonts, it does not save the settings. The apply button is greyed out when font settings are changed. When re-opening the setting, the settings are back to the original state without any of my modification to the settings. I've also tried restarting the machine upon modifying the setting. I am essentially stuck on font size 6 without any way to change it.

STEPS TO REPRODUCE
1. Open Plasma Desktop Setting
2. Go to Font Management in Setting
3. Adjust Font Size or Forced DPI Setting

OBSERVED RESULT
Apply button greyed out and nothing in the setting is saved.

EXPECTED RESULT
Apply button should not be greyed out and should save the settings upon clicking on apply and the effect should be seen after restarting Plasma Desktop.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux (Latest today) 5.18-1 plasma-meta package
KDE Plasma Version: 5.18
KDE Frameworks Version: 5.67.0
Qt Version: 5.14.1

ADDITIONAL INFORMATION
Prior version 5.17.90 does not have this regression.