Created attachment 127930 [details] screenshots In kcm_icons, the GTK icon theme cannot be configured independently from the KDE icon theme. This is in contrast to the application style (kcm_style), where the GTK2 application style, GTK3 application style, and KDE application style can be chosen independently. Not being able to configure a different icon theme for GTK applications and for KDE applications is problematic because KDE icon themes lack icons that some GTK applications depend on and GTK icon themes lack some icons that KDE applications depend on. This leads to missing icons or inconsistent icon styles within an application when fallbacks apply. The screenshots show missing icons in Dolphin’s toolbar when using Adwaita and an inconsistent icon style in Evolution when using Breeze. In previous versions, the GTK icon theme could be configured independently of the KDE icon theme.
That's right, GTK apps uses the general icon theme now. Strictly speaking there is no such thing as a "KDE icon theme" or a "GTK icon theme"; icon themes are inherently meant to be cross-desktop-compatible. So we thought it would make sense to just configure the icon theme settings in one place and apply it to all apps evenly. If icon themes are missing icons, that's an issue with those themes that should be reported to the theme creators.
Icon themes are not required to ship with all possible icons, because the XDG icon spec defines inheritance. Unless it is possible to inherit from both KDE and GNOME icon themes at the same time, users will expect to configure icon themes separately.