Unless you go through the effort of setting up ProtonMail Bridge so you have a local IMAP / SMTP bridge for ProtonMail, not possible. ProtonMail only offers SMTP (no IMAP) for Proton Business customers, with IMAP only being possible with the bridge. So you’d have to run the bridge then have the Mail app connect to that.
Your easiest option is the Android app (aside from getting a C2 of course 
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