Do the forces behind Proton Mail trade in user information and search messages for information they can store and sell to other entities? I have avoided gmail because they do that (as do a lot of email services.)
I have been using Gmail for 10 years or so and I have never had a problem with spam. I get some unwanted mail from sites I have dealt with but that's easy to stop. I don't think its Gmail causing your problem, I think your email address has been compromised.
I use both gmail and protonmail. Both are encrypted. Gmail is eminently accessible to the constabulary, and I would suspect that everything written there sits on a US government server out in the southwestern desert, just like phone calls here in the US. If they have any problems getting your communications, Google will obligingly cough them up. Protonmail sits on a server in Geneva, Switzerland. If you use a VPN to access it, you are probably OK. If I understand correctly, changing your password, whether it is your idea or under duress, will delete everything in your account. I have never had a single run-in with the law, except for my perennial speeding tickets (Cogito Ergo ZOOM!), but it seemed like a good idea to have a Protonmail account.