Gajim is _okay_ on desktop, but it leaves a LOT to be desired. Everything else feels way too bare-bones to feel comfortable recommending to Discord expats. Fluux Messenger is the closest I've seen, but it's sluggish for me. Maybe that's just Tauri on Linux.
Conversations is good on Android (bit barebones feeling), and I haven't tried out voice with it. IDK what the situation is in the Apple ecosystem.
I really, really wish I had the time to just start building a strong suite of XMPP clients. Every day Discord shoves a new ad in my face I get closer to biting the bullet.