• Just like Google it has an app and a web interface. Seeing that OP is looking to replace Google and didn’t mention self-hosting, this seems a good fit.
• Proton does provide e2e encryption.
• What does US citizens using it have to do with anything? Proton is not based in the US.
• Your last point is a maybe and remains to be tested in practice. If this is a concern, then take it into account.

For me personally it is more important that my data doesn’t get mined by a big company, and that I use European services as much as possible, and preferably open source. Proton is a good fit for me, and may be for OP.

I like Proton. It’s secure, with end-to-end encryption. It is web-based, just like Google, so accessible anywhere. It has an eye-pleasing design. And it’s based in Europe.

Oh, it’s perfectly clear. We got the message. Mozilla are not to be trusted with our data.