Signal is incredible user friendly, privacy respecting, the gold standard for encryption, cross platform, etc. Yes, it’s centralized, yes it’s imperfect in many ways, but it’s easy and it’s pretty damn good.
If you want to help the people around you to become more involved in understanding and owning their tech, it has to be an easy and good experience. It has to be tangibly better, not just abstractly better with tangible downsides.
I use XMPP, but would never try to convince my friends and family to use it; it’s too complicated, the user facing apps all suck (Snikket and Cheogram are the best of the bad lot), and the incentives to use it aren't there. As you said, it’s just not attractive to a regular user, since it’s all around a worse experience than what they currently use. The one exception is that I do occasionally recommend XMPP for SIP access via jmp.chat to some of my more technical friends who have a tolerance for clunky user experiences in favor of privacy and affordability. I am holding onto an unreasonable hope that Signal or Whatsapp or others will consider XMPP+OMEO in the future to popularize the standard, but that is extremely unlikely.
Matrix also is an unfortunately terrible alternative to discord (even Element is a rather lacking user experience), so while I have pushed to move groups there before, I no longer recommend Matrix. I suggest signal or nextcloud as alternatives when possible; the remaining large groups who need the closed server forum style system are usually unlikely to move to Matrix anyway.