Nowadays doesn’t even make any sense to use servers. ... Why not create something better?
i think you might underestimate the problem.
Jami.net (a decentralized messaging app) works p2p. it uses a torrent-like distributed-hashmap to locate the peers at any moment. (The main usability issue for nontechnical users, is that devices on an internal ip address aren't addressable from outside. This requires (a single point of failure and privacy concern), a turn-server)
They started to incorporate Git for merging chats for the reason that any of set of peers (of a group chat) can be out of reach of another set of peers, i.e. the chat continues on different branches and needs to be merged again later.(this happens in the clients-app, because there is no central server). Jami is aiming at double-digit group sizes.. That's not nearly the size of what Lemmy is handling.
Here's a howto https://lemmy.ml/comment/459391