I hope it won't take too long until this is implemented. It's baffling that such a thing is not possible in an easy and accessible way and instead is hardcoded.
I only have one email address from ProtonMail but I make extensive use of their "Additional Addresses" feature and I use ProtonPass email aliases. There are only a few sites which know my real email address (around 15 I think).
Edit: technically I also have a Gmail address but I'm trying to get rid of that since it has my deadname in it.
I hope it won't take too long until this is implemented. It's baffling that such a thing is not possible in an easy and accessible way and instead is hardcoded.