ArcGIS Feature Service connections which have their corresponding Portal endpoint URLS set can be explored by content groups in the browser panel.
If a connection has the Portal endpoints set, then expanding out the connection in the browser will show a "Groups" and "Services" folder, instead of the full list of services usually shown. Expanding out the groups folder will show a list of all content groups that the user is a member of, each of which can be expanded to show the service items belonging to that group.