What you’re suggesting is that everyone can see all of the groups but when they join one they can no longer see any groups? I can’t quite imagine how that could work.
Not like this, but you gave me an idea, it would be better if I couldn’t see those groups (B,C) anymore once I have selected one (Group A), it would be like the title option that could only choose one, but no longer had the option of being able to select another (of course the staff can change it in case you have made a mistake or something like that).
If you don’t want users to know about the other groups then you’ll can just make the groups not visible to anyone and manually add them.
Not really, I think it would be more work, because I think I would have to be creating a topic where they would request these memberships and have to be reviewing each profile.
It had also occurred to me to create a custom field, which when selected automatically would give it access to certain categories, I couldn’t find anything similar either and I take the opportunity to ask if there is something similar, a plugin that could perform this function.