@feditips
I looked into Guppe and Chirp. I'm on Friendica, missed that there were 'Friendica groups'.
But, Guppe & Chirp were not quite the same type of thing, though they do look useful for other stuff. The Private FB Groups, you need to be approved by a moderator to join; and you can only see the posts in the group if you're in the group; and discussions are sorted into threads not so much individual posts like mastodon & friendica - akin to oldschool forums with the permissions set up so you need to be logged in to see the posts, just without each forum needing to be a separately hosted website people need to manage individual accounts for.
Hmm. It sounds like so far there likely isn't a federated equivalent for me to ditch the things I use Facebook for. That's unfortunate. I will keep an eye out for "Mastodon Groups" and see how close it gets to the "'private' communities" I use Facebook for. Guppe Groups and Chirp Groups might work for more simple 'public meme group' equivalents though. I guess my Facebook account stays for now, unless Friendica Groups will do the thing. I will look into its functionality. Thanks. 💖