If you use Jabber today, who are you talking to and on what server(s)?
It seems to be a good fit for families. Or rather, families are a good fit for any sane, sustainable technology. Long span of time, lots of mutual transparency, plenty of in-group communication inside and outside the chat technology.
No problems characteristic for big-tech (account seizures, hardware platform restrictions). No problems characteristic for free-for-all public servers (spam, vandalism).
XMPP for me is mostly internet friends. It's quite popular on the fediverse (they also happen to commonly dislike Matrix, although many are on both like me). Lots of people who are into technology and anime, basically.
I've noticed most free software projects don't have an XMPP room unless they are literally XMPP projects like Gajim and Dino. Pine64 (as well as many other places) will have a bridge between IRC and Matrix, but I've only seen one or two IRC channels that also bridge XMPP that I can remember. Many people aren't even really aware of it. I don't know the actual stats, but it often feels like XMPP is actually less popular than IRC these days.
I run my own server (any 5 bucks VPS can do), but there is a large number of public servers that also work good. Make sure to pick one with a good ranking at https://compliance.conversations.im/
(I will add that Jitsi Meet kind of counts as Jabber use, although not in the traditional sense)