And virtually everyone else, right?

What is open standard used today?

XMPP is still alive (= there is a community maintaining protocol, clients and servers). I am using XMPP exclusively for chat since about one year, pulling in most of my friends. It seems that if users do not demand the usage of Internet Standards like XMPP we will be stuck with corporate walled gardens forever. See also: https://blog.samwhited.com/2019/02/whats-wrong-with-xmpp/