Simply use free Usenet Servers via Tor and post your anonymous* PGP messages to the Usenet group alt.anonymous.messages.

*You send PGP encrypted messages via Mixmaster Remailers (via Tor) and preferably use a hashed subject (hsub) so that the intended receiver(s) can filter out their messages.

https://lists.gnupg.org/pipermail/gnupg-users/2019-March/061...