This has been asked at User Voice

Over 2900 votes on User Voice https://protonmail.uservoice.com/forums/935538-accounts-payments/suggestions/33188971-accept-monero-for-payment

So if that isn’t good enough I can’t see a Change.org making a difference.

They already had a controversy some time (years?) ago, saying stuff like “Bitcoin is all we need”, “everything other than Bitcoin is a shitcoin”, “we don’t want to associate with the criminal record Monero carries”… something like that.

What you can do is to use non-kyc exchanges, send XMR in, exchange to Bitcoin, and withdraw directly to Proton. Proton won’t be all hurr durr about dirty Bitcoin.