Exchange Online supports hidden membership for Microsoft 365 Groups and distribution lists. Hidden membership means that no one except members and admins can see who’s in a group. It’s a useful feature if you don’t want people poking around to find out who’s in a group or distribution list. One thing to be aware of is that once a Microsoft 365 group has hidden membership, it has it forever. Distribution lists on the other hand can flip between hidden and visible membership.
https://office365itpros.com/2022/10/04/hidden-membership-groups/
