I have been using Protonmail (infrequently) for a few years in the event the S&P 500 goes to 0, bullet cartridges become the world, and cans of spam become the new hotness. Essentially it is end-to-end encrypted email with a moderate amount of file storage. This means that neither Protonmail nor other unintended receipts cannot read your messages. Protonmail does not maintain a list of user passwords. As an added security feature/inconvenience, after logging in to the service, you have to unlock your mailbox.
I won’t and can’t go into a full description of the service, but if nothing else, Protonmail doesn’t parse my email to suggest sentence completions. Additionally, Google will parse your email for travel dates, appointments, and purchase history.