Glade 3.22-1 GTK UI builder has a bug: there is no GtkScrollbar in Containers menu. See also https://gitlab.gnome.org/GNOME/glade/issues/302
To get GtkScrollbar selection back into menu navigate to /usr/share/glade/catalogs and edit gtk+.xml file:
- find line
<glade-widget-class-ref name="GtkToolbar"/>
- insert new line
<glade-widget-class-ref name="GtkStatusbar"/>
after it.
Cheers!