It’s a matter of process for different user groups on the forum, not meant to be “mysterious.” Sorry you haven’t been briefed on groups yet. If you want, I’d be happy to hop on a Slack call and answer your questions. These are all a bit construction-era inside-baseball admin details that aren’t relevant to the community-focused mission of CET, as far as I know.
For Science Collaborations, we agreed on a process where in the onboarding for a new SC member, they can create a Community forum account, and then click on the button for their SC’s corresponding group to request membership. The SC chair is also the owner of that group, and can accept the request after cross-referencing their membership list. That system was designed to help the SC’s self-service their use of the forum. That group membership in turn, gives the SC member access to the SC’s own closed category, which SCs can use as an alternative to a traditional closed email list.
For other groups, like the “lsst” staff group, we have a process where the individual managers are supposed to add their team members. For Data Management, here’s the bit from our onboarding procedure. These are “closed” groups because the group owners do the management.