Gtk.IconSet.new_from_pixbuf

function new_from_pixbuf(pixbuf:GdkPixbuf.Pixbuf):Gtk.IconSet {
    // Gjs wrapper for gtk_icon_set_new_from_pixbuf()
}

Creates a new Gtk.IconSet with pixbuf as the default/fallback source image. If you don't add any additional Gtk.IconSource to the icon set, all variants of the icon will be created from pixbuf, using scaling, pixelation, etc. as required to adjust the icon size or make the icon look insensitive/prelighted.