Proton is definitely no good. Ads, freemium, AI garbage, Bad 3rd party client compatibility, CEO loves Trump, collecting excessive metadata that they are then regularly forced to hand over to the cops, etc.

Its better not to put all your eggs in one basket so dont try to find a single provider for all your needs.

All email services will be able to read your emails unless you encrypt them yourself (PGP). So there are no “private” email providers really. What you should look for is just a functional provider that works well with proper clients like Thunderbird (available for desktop and mobile).

This is a list of many tried and tested servers, just pick any of the “OK” ones: providers.delta.chat
Deltachat is an app that allows you easily use email in and end to end encrypted way while making it look like a standard instant messenger. For this to work properly the provider needs to support 3rd party clients properly, so this list gives you a good look at the technical quality of the email provider.

See how Outlook, Proton and Tutanota are non functional? Thats because they dont implement the email standard properly in order to lock users into their platform and apps.