If you mean the #fediverse then I don't think there's one predominant messenger.
Having said that a lot of people use #xmpp with #OMEMO
Discussion
I just headed Obi Nwosu and Renata Rodrigues talk about how nostr and matrix were a part of Fedi. https://youtu.be/FCvDLjZ6ePM?si=NyI3JujfwOiKAO97
heard*