They implemented their own way of doing this. They don‘t use PGP. I don‘t know how it exactly works, but it‘s open source, so you can look at it yourself.

Subject lines are also not encrypted, unlike Tutanota.

Dude, Norway is one of the richest countries in the world.

Yes, but it still protects against data breaches. You still have to trust the provider though.

Proton Mail does not encrypt the subject line afaik.

But yes, the content is encrypted.

DuckDuckGo results still suck and are not even remotely comparable to Google‘s. The best alternative imo is Qwant, which uses bing and I think also it’s own index.

I wouldn‘t use it for messaging, but as a social media platform it seems to be working pretty well.