Sometimes you don't need a P2P VPN, but rather a P2P stream manager (eg. BitTorrent).

A somewhat nice solution for that is Iroh (QUIC P2P w/ hole punching): https://www.iroh.computer

They also provide a solution to discoverability: https://www.iroh.computer/docs/concepts/discovery

Which boils down to storing ECC signed arbitrary data on the mainline DHT.

Two showcase Iroh utilities that are actually useful in practice:

https://github.com/n0-computer/dumbpipe

https://github.com/n0-computer/sendme