It is really cool. And needed.
I am wondering if friendica needs a gui update, since it has groups since ages. But I do prefer pixelfed over friendica.
You can give https://pi-hole.net/ a try. If you are able to set up a raspberry Pi and follow instruction of the documentation 🙂
I use it regularly. There are some problem with key exchange in group chats. Sometimes users have to write messages to each other via direct message then everything usually works: so if users in group chats do not know each others, that can cause problems:
Concerning clients: Android: conversations Windows/Linux: Gajim Debian and other Linux distros: Dino
Concerning apple I do not know.
There is the promising snikket.org project who have a “product” approach, i.e. they are developing clients with the same look and feel for every client. But unfortunately, they are not there yet. But as far as I know they have funding.
XMPP is easier to selfhost than matrix. And it can run on a Raspi. You can install a xmpp server with e.g. yunohost, to make thinks simpler.
Just for reference: https://medium.com/we-distribute/the-do-everything-system-an-in-depth-review-of-hubzilla-3-0-692204177d4e
Forum channels are particularly noteworthy because they are analogous to Facebook Groups.