Nobody ever talks about S/MIME, but it's the corporate version of PGP/GPG for mail. Apple made it dead easy to use S/MIME encryption. Most vendors do, because it's still a requirement for some government purchasing (DoD is moving away from it). I was honestly and pleasantly surprised how easy it was to use S/MIME with the built-in mail programs on macOS and iOS/iPadOS, and I'm a bit surprised that Apple didn't just automate an S/MIME key for every iCloud mail user.