Maybe not intended to be, but they work fine as one [ime]
Revolt can be self hosted, but i'd still consider it centralized, since when we are talking about "revolt" we are talking about the main instance. I haven't seen another instance sadly
However the devs are working on E2EE, and they [no promises] said they'll think about implementing federation. I'll keep my eyes on it, because if it does i'd definitely be excited for that
Matrix/Element (or whatever app you like), whilst not a direct alternative to Discord is very close to it. And the fact its E2EE and decentralised makes the minor differences much more palatable. Revolt have been promising E2EE for years and yes I can see its on their roadmap but at this point I doubt it'll be here in the next year or two, if ever.