Mastodon has no sense or support for groups whatsoever.

Mastodon aims to be purist, old-school microblogging. Anything that isn't purist, old-school microblogging has no place on Mastodon. Not even enclosed threaded conversations. Especially not groups. For Twitter has no groups either.

The result of this is that the huge majority of Mastodon users don't even know that there are any groups anywhere in the Fediverse. What they can't see on Mastodon doesn't exist at all.

FediGroups is kluged Mastodon, but it sells itself to Mastodon users as the only group solution in the Fediverse. And Mastodon users buy it because it's literally all they know. Come up to FediGroups with something like Friendica or Hubzilla or the Threadiverse, and they'll still insist that FediGroups is vastly superior to all of them in every way imaginable. As far as I can see, FediGroups was invented by Mastodon users who at that point had never even heard of Friendica or Lemmy, who might even have believed like so many others that the Fediverse equals Mastodon.

On the other hand, Mastodon is rumoured to be working on groups itself. But knowing Mastodon's track record (as well as Mastodon's philosophy of trying hard to make the non-Mastodon Fediverse look broken and therefore very undesirable to Mastodon users), we have to expect Mastodon re-inventing the wheel in a way that's as incompatible with existing wheels and roads as it ever comes.