I've had a lot of people ask if mutt-wizard can work with ProtonMail's encypted mail. The old answer was "No", but as ProtonMail Bridge has become a thing, it's now possible to have your mail from ProtonMail offline, including in mutt.
ProtonMail Bridge requires a paid account to use, but if you have one, I encourage you to try it with mutt. I've just push a commit that should give mutt-wizard compatibility with ProtonMail and PM Bridge. Since I don't have an account with them, I can't test it, but I invite everyone who does to try it once you have Bridge set up and tell me if it works as expected ;-)