I've set a group to Public Approval. The info says "Anyone can join but must be approved". That seemed appropriate for what I wanted.
However when I set it to this, and send someone the group link. They do not see a join option. I've recreated the group a few times. The same problem persists.
It would also be nice if there was an option to change it from Public, Public Approval and Private on the fly instead of having to delete and remake the group. That way I could just go with Public for now and change it later when the issue is resolved. But I guess that's a topic for a different thread.