Back out fallback icon support which does not work as intended The fallback icon support does not work as intended since it depends on gtk_icon_theme_has_icon() in order to determine whether an icon exists in the current icon theme. Contrary to the documentation GtkIconTheme not only falls back to the "hicolor" theme but also to the "Adwaita" and "gnome" themes when looking for icons. The Adwaita theme provides the "system-software-update", "software-update-available", and "software-update-urgent" icons so the fallback will never be used even if the current theme does not provide these icons. SNI host implementations such as the one in KDE Plasma Shell will only look for icon names in the current theme and do not fall back to the "Adwaita" and "gnome" themes.

[Desktop Entry]
Name=Package Update Indicator
GenericName=Package Update Indicator
Comment=Notify about available software updates
Icon=system-software-update
Exec=package-update-indicator
Terminal=false
Type=Application
Categories=Utility;GTK;TrayIcon;
NotShowIn=GNOME;