This is how it looks on my side.
(don't follow that actor please, it won't work, the code to handle most of group federation is yet to be written)
You can now follow that actor from Mastodon (and any other #ActivityPub server, probably), and you'll even show up in the group members list, but doing so still won't be of much practical use.
(don't follow that actor please, it won't work, the code to handle most of group federation is yet to be written)