The issue is group owner(not global admin) can't see all widgets in the list of the sidebar panel when the group page is in edit mode.
For example: the group owner can't find OOTB "Navigation List" widget in the sidebar panel.
The previous Telligent version has a special "Widget Availability" panel in the admin panel which helps resolve that issue. It seems that Telligent 12version doesn't have that panel anymore.
Does anyone have any idea to resolve that issue?