I would go kde plasma everyday. I always find little things that limit what I am trying to do on cinnamon.

Not big things, little trivial things. An example is wireless hotspot. I cannot change the password through the gui. Why? Dunno. Deal breaker? No. But those are the little things that kde has right.

Not sure about xmpp, but definitely matrix

I’m using cinnamon, but want to use the new plasma on a debian based distro. But nothing is supporting it out of the box just yet.

But yes, there are a lot

Beeper can bridge those into a matrix chat. Then at least you can chat with people who or on a privacy related one as well as the heathens in Facebook messenger