Moved form https://bugs.kde.org/show_bug.cgi?id=501436 if on icon theme available "foo-symbolic" 22px and "foo" 32px icons - the "foo-symbolic" icon will still be used for hidden menu, ignoring the dimensions and scaling the icon from 22px to 32px size. Reproduced on hide menu tray widget. Tray icons used "Kirigami.Units.iconSizes.medium" But hide tray menu use "Kirigami.Units.iconSizes.smallMedium"
Created attachment 179395 [details] Klipper example
if icon theme use 22px "Kirigami.Units.iconSizes.smallMedium" icons for tray monochrome (-symbolic suffix), but for 32px colorfull "Kirigami.Units.iconSizes.medium" anyway Hide Meny Tray Widget use 22px stretched and zoomed "-symbolic" icon from 22px to 32px and ignore that non -symbolic 32px icon available on icon theme. See example on attached file. "klipper-symbolic" 22px used on tray - good! it's "Kirigami.Units.iconSizes.smallMedium" "klipper-symbolic" 22px stretched and zoomed to 32px for hide menu tray widget - bad! it's "Kirigami.Units.iconSizes.medium" "klipper" colorfull 32px available on icon theme but not used on hide menu tray widget
The idea of the implementation is to use small 22px icons with the suffix "-symbolic". But for larger sizes of 32px, use a colorfull icon. On Plasma 5 it's possible doing with plasma theme. But now icons from plasma theme not used!
Created attachment 179413 [details] logic work
I think this makes sense. If the icon loader returns foo-symbolic at a smaller size, we know it will be scaled up and become blurry. Probably better to return a correctly-sized non-symbolic icon than to get a blurry symbolic icon.