https://www.privacyguides.org/en/email/
The wiki lays it out pretty well. Since you're interacting with normal people all your emails are both sent and received in the clear and can be read by your email provider and your counterparties email provider.
As far as Google alternatives go fast mail which isn't an encrypted email service is a reasonable alternative that lots of people enjoy.
The big difference between proton and Tutanota is what is encrypted at rest.
Proton does not encrypt subject lines to and from lines at rest. So that means they can always inspect who sent you mail and what the subject was. The benefit of this is indexing as fast and you can use their search quickly.
Tutanota does encrypt everything at rest. So nothing is readable including subject to and from lines. Except by your client with the correct key. You can search your email locally but you have to maintain a large cache of your email if you want to search all of it.
As far as encrypted email goes it's great, but only for encryption at rest, if it's caught in live transmission then the data's compromised. But it's definitely better than leaving the data open on some server. So the choice is yours