SUMMARY When changing the font page settings, there is no way to apply the changes. The apply button has no way to click. When exiting and entering the sources page, the page returns to the standard it was in. STEPS TO REPRODUCE 1.Make changes to font options 2. 3. OBSERVED RESULT The apply button is then available to select. EXPECTED RESULT That the changes made be applied. SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: 5.4.15-arch1-1 (available in About System) KDE Plasma Version: 5.17.90 KDE Frameworks Version: 5.66.0 Qt Version: 5.14.0 ADDITIONAL INFORMATION First photo shows the original configuration. And the second photo shows the changes made and the Apply button is not selectable.
Created attachment 125474 [details] first photo
Created attachment 125475 [details] second photo
Looks like an Arch problem with plasma-integration, cf. also https://bugs.archlinux.org/task/65291
Oh, wait, I was focusing on the missing QtQuick Controls 2 style but since plasma-integration is also involved in fonts I'd say this is still that distro bug.
The referenced downstream bug has nothing to do with the apply button not being enabled. Also, it affects Qt 5.14.1 only and the OP is on 5.14.0
*** This bug has been marked as a duplicate of bug 416358 ***