I was big fan of xmpp until I have to admin our company internal server (can ignore all the s2s stuff).
I was surprised how poor is a basic protocol description. Any functionality expecting from common messenger is provided by some protocol extension (XEP).
Many of them never have passed "draft stage" touched last time 15y ago. It's not easy to find server and client supporting some pretty list of XEPs. We are using pidgin client (Linux+Win support) and I'm pretty tired answering questions like "I want feature XXX I can use on my Miranda". My typical answer is "sorry, Pidgin just cannot do it". Or "this is unaccepted protocol extension (XEP) and every client implements it different and uncompatible version."

Yes. If you want to send simple text message, it's fine.

But it's mostly abandonware. 

 Pidgin is the oldest and least worked on client.
XMPP is like Nostr.  To say “Pidgin sucks so XMPP sucks”, is like saying “Iris sucks, so Nostr is abandonware” 

 Will be glad for any recommendation of good client with Linux+Windows version. 

 Gajim 

 Installed. Will give a chance for a week. 

 ok cool 

 Returning back to pidgin.
Besides nicer pidgin's GUI that is just matter of personal preferences, I really don't like on gajim (1.1.3 @ Ubuntu 20.04.6 lts):
- no automatic join to chat rooms after connection to server
- advanced option "tabs_position" is ignored or is doing something else I would expect from the name
- incomming messages don't raise chat windows automatically. Missed few important messages
- during logoff I am getting warning that there are some unread mesages but I have no clue who written them (see previous point)

Gajim is now on my list "let's try it again in few years". 

 Gajim is Windows/Linux.  Dino is Linux only and cleaner. But you asked me about cross-platform.
The whole different clients thing is a decentralization thing. 

 In a company supporting 2 OSes for employees, you still want to support just one messenger. 

 You won't miss messages on Dino.  For Gajim, maybe notifications, but it will still be on the list panel 

 Yeah I understand where you’re coming from.  I do.
I’m just saying XMPP is more private, decentralized, and the user has more control 

 Just for clarification - I didn't mean "the xmpp is abandonware" is based on quality of pidgin. This my sentence is based on release dates of XEPs and the big number of them (generaly implemented across servers and clients) never moved from "draft" stage.