XMPP (with omemeo) is the classic (and also what FB messenger uses behind the scenes, without omemo), Matrix is the new kid on the block taking over. Both are decentralized sorta like the fediverse (but separate from said fediverse.)
Used to use Signal, but they're removing SMS support so everyone might as well switch to matrix. Wickr was bought by amazon (and they say they won't ruin it, riiiight), so that's out. Idk enough about briar or session, and telegram isn't as secure as people seem to think.
I hear this one too and honestly, it does negatively effect them, they just don't see it because it feels like it's always been there. But give them ad-block for a week and then take it away...