And to add to @[email protected]’s info about setting up XMPP here is a ansible playbook that you could use to deploy matrix: https://github.com/spantaleev/matrix-docker-ansible-deploy
I would look at what you want to use it for and see if you can do that better with XMPP or Matrix. The factor that is keeping me on Matrix is that I have all diffrent chats with people on different platforms in one client that is cross platform. Here is the list of available bridges in Matrix to get other chats into it: https://matrix.org/ecosystem/bridges/
But keep in mind that is is against ToS for most apps, so there is a small risk of getting banned from other platforms. I can only tell you that I’ve been using it with WhatsApp, iMessage, Discord and Signal for half a year and am not banned anywhere. That is with running my own Matrix Server and bridges on a rented VPS.
For information about what XMPP can do you’ll have to do research on your own as I don’t know anything about it besides that google kinda “killed it”.
There is some truth in it, they reduced the iPhone Box size, so they can ship more iPhones in the same amount of space thus reducing emissions for transport. What they should have done tho is allow people that buy a new iPhone or iPad to get a charger for free if they want them. That would still reduce emissions from transport… but they choose the way that people would need to buy a charger and with that also sneakily increasing the iPhone price by removing things that were included with earlier iPhones. (charger $19 + EarPods $19 that are no longer included with modern iPhones).