A lot of clients have OMEMO on by default now. You can’t enforce it for all clients & across the entire network tho as XMPP is a ‘simple’ protocol without a let of bells & whistles meant to be eXtended like OMEMO/OTR/PGP built atop it. With the newer compliance suites tho, to be considered ‘modern’ OMEMO & other e2ee options are expected to be supported. Gajim makes the UI easy, & Conversations isn’t bad. Profanity is a bit more obtuse to use since you need to trust your own keys manually too & they’re not autocompleted, but all the tools are there even for a TUI client.