Both libgtk3-perl and libgtk2-perl are not in main. libgtk2-perl is in main in Zesty and later once gnome-software recommended it on 10 Apr 2017. However, it didn't get a MIR.
Both libgtk3-perl and libgtk2-perl are not in main. libgtk2-perl is in main in Zesty and later once gnome-software recommended it on 10 Apr 2017. However, it didn't get a MIR.