Despite only being validated in February, I think Group federation has been a smashing success for the Fediverse.
I use Fediverse groups every day.
And if you’re interacting with this post, so are you.
Fediverse groups even make Mastodon that much more extensible despite Mastodon itself not officially supporting groups yet.
https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-1b12.md