First, no, I would never advise that anyone use ProtonMail, and if your primary objective is to gain security, I wouldn't recommend FastMail. The comment you're replying to provides the reasoning for that.

For most people, including technically inclined people, running your own mail server will almost certainly lose you significant amounts of security.

If you deal with sensitive documents like legal artifacts in immigration cases, you want to have control over which of your documents wind up in the cloud and which you retain custody over. So while viewing attachments in the cloud is very good practice (viewing them locally is a good way to get owned), running a service that generally slurps your local drive (or big chunks of it) into the cloud is not a good idea.

If you want to run a Chromium build rather than Chrome, that's fine.

I provided the reasoning for preferring iOS devices to general purpose computers already. The additional concern you just added doesn't come close to offsetting.

I'll add, though this isn't in the Tech Solidarity checklist, that if the goal is commercially reasonable security and not security in the public interest, Chromebooks are another good option for end-user computing.