- open icons kcm - install icon theme - install button becomes uninstall button what happens: the uninstall button has additional options in the dropdown menu. that additional option is use. without context it is not clear what this means or does. from some testing I am inferring that it sets this as the default icon theme but this is not particularly obvious or communicated, nor does it make any sense that the 'use' option would be hidden in a dropdown of the uninstall button. it has nothing to do with uninstall... what should happen: the use button should be a checkbox or dedicated button, or just not be there (relying on the invoking software to have a means to select the used entity?)
Created attachment 108404 [details] screenshort of Plasma 5.10.5
Currently there is no usage of this weird use button known to me. Also most KCMs are/have been ported away from the QWidgets dialog to the QtQuick one. There the "Use" functionality has a dedicated button.
This is indeed a very old thing that has been fixed since, by using the QtQuick bits in place of the old widget based stuff. Since the widget stuff is effectively on life support, and how much work it'd take to rejig this in the widget dialog, i'm calling this one fixed (especially since the icons kcm specifically has been switched to the qtquick components).