The guy who wrote the OP is the guy behind Signal. That's the most obvious alternative. But there's not a go-to answer because the lesson learned from PGP is t

The guy who wrote the OP is the guy behind Signal. That's the most obvious alternative. But there's not a go-to answer because the lesson learned from PGP is that there can't be a single crypto Swiss army knife of a protocol. There are conflicting tradeoffs that necessitate the use of different protocols for different use cases. The best replacement for PGP is probably a basket of different protocols. See for example: https://blog.gtank.cc/modern-alternatives-to-pgp/ https://blog.gtank.cc/modern-alternatives-to-pgp/