Organisations, groups, and projects can have members and followers in private ecosystems. The admin of the organisation/group/project can decide the privacy settings when creating the organisation/group/project.
The privacy settings can be set as below:
By making your organisation/group/project semi-private, you allow members of your ecosystem to request to join the group.
By making your organisation/group/ project private, your ecosystem users can only view or join the group by invitation.
Usually, the organisations/groups/projects are created as private on private ecosystems, so users can only join by invitation and if they are not invited, they can only follow the organisation/group/project.
On the other hand, when these are created as semi-private, users can send join requests to the admin, but they can also follow.
📝 Note: You can always update the privacy settings of your organisation/group/project from the Settings section.