>>88066863PGP is not a very secure option because it entirely lacks forward and future secrecy. Same goes for schemata derived from it, such as OTR. Use double ratchet based encryption protocols.
If you want proper fully decentralized messenger, use something like Briar instead. You can even use adhoc networks of any kind, including bluetooth, Tor or SD cards carried by pigeons, while benefiting from an actually secure protocol and an okay app. However, this will still be barely usable for most people, since it requires you to be online to receive messages, which is exactly why things like (non-P2P) Matrix, Signal, etc. use servers.