Created attachment 177519 [details]
Screenshot with annotations illustrating the affected areas where keyboard focus seems to misbehave

SUMMARY

When using the builtin Windows 9x theme of KDE and a dark color scheme, it seems to be that 50%+ of elements in the KDE system settings don't render any sort of keyboard focus at all, requiring to press tab followed by space or arrow keys to mess around until something reacts and you figure out what is focused. Some other elements seem to render the keyboard focus using a wrong color, using black on dark gray rather than white. Only the search box seems to work as intended. While this could be blamed on the theme, most popup dialogs seem to have a perfectly working white on dark gray and easy to see keyboard focus on all the buttons, so this seems to be some KDE system settings problem. However, e.g. Spectacle is also affected.

STEPS TO REPRODUCE

1. Choose builtin 9x theme for application style
2. Choose Materia Manjaro Dark High contrast as Colors style
3. Check the regular settings UI in systemsettings for keyboard focus behavior, and compare to any popup dialogs like e.g. the "Pair New Device" dialog in bluetooth settings where it works as intended

OBSERVED RESULT

In most settings panes, the keyboard focus doesn't seem to be working as intended. It's either not visible at all, or barely visible with wrong colors. In the popup dialogs however it works, suggesting that the color theme was meant to have a proper focus color set. Also, when I try other dark color styles, the problem seems to persist.

EXPECTED RESULT

Keyboard focus works directly with dark color styles combined with the builtin 9x application style.

SOFTWARE/OS VERSIONS

Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: postmarketOS v24.12 based on 3.21.2 with kernel 6.12.9-0-edge (64-bit)
KDE Plasma Version: 6.2.4
KDE Frameworks Version: 6.8.0
Qt Version: 6.8.0

ADDITIONAL INFORMATION