What a bunch of hype garbage this is. If you send something in plaintext to a server it's already game over. If Google was serious about privacy it would pgp-encrypt everything so only the client, client-side can decrypt it, just like what protonmail does. pfff, 'self destructing emails', what a heaping pile of razzle dazzle no-ops that is -- this is more likely subliminal advertisement for the new mission impossible…
I feel like client-side email encryption is a missed opportunity for Apple. Easy encrypted email would fit nicely into their narrative of “we can offer privacy features that Google can’t, because we sell you stuff”
Apple supporting it won't help apple users one bit, because nobody else uses an actual application to check mails anymore. It's mostly web mail clients everywhere, and they obviously can't use encryption.