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).
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