While far from being the best solution and us only settling with it after RetroShare wasn't working on my friend's side, I went with Tox. I wouldn't recommend it to the radical paranoid who's aware that the protocol still hasn't undergone a proper audit and also no longer offers many actively-maintained clients, however it's enough for our use case.
It's quite sad that P2P nowadays mostly means some Crypto-nonsense. Classic P2P chats went out of fashion in favor of Discord and other client-server services (that may or may not be routed through Tor, which... I personally trust even less).
adding onto this a bit: before i made the client-server protocol chat2me, i made a peer-to-peer client inspired by the likes of ed and classic phone calls where you had a direct line connected by an operator.
i called it p2pc, and i still have the source code if you want to email me over at sbcv.co.uk. it's entirely plaintext unextended ASCII using TCP/IP; all you need to chat to someone else is an IP and the port they're listening on!