I think you still can pay. 
here is a link:
https://proton.me/support/pay-with-bitcoin 

 Your link says: "Bitcoin is not available as a payment method during account sign-up" 

 nostr:nprofile1qqs9hejyd252x8q3kw6980ud4lymx3hlx2x3lgg6p7sz58nyv8m2nvgpvemhxue69uhkv6tvw3jhytnwdaehgu3wwa5kuef0dec82c33wscxu7t8xc6xwdtkwac8yanpx5e8wmrrd46rwentv3erqdmkx4j8ydmnxv6hyct389nnq7r8vvcxkdrcvdek2er2vachv0mzwfhkzerrv9ehg0t5wf6k2qg5waehxw309aex2mrp0yhxgctdw4eju6t0qyg8wumn8ghj7mn0wd68ytnhd9hx2ujnh08 said it already haha after that phrase it to say that you can 😅 

 privacy.com helps 

 >  Are they just a CIA honeypot all this time?

This is the question I am starting to hear from privacy educators now because they have added a bitcoin only wallet. I think that's a question we should always ask but I'm not sure if they are or not. 

 I stand corrected. There is a free option here that I didn't see: https://proton.me/mail/pricing 

 Every time I tried to open a free account behind a VPN, they asked for SMS verification. In their documentation, they claim its to prevent abuse. In my experience, they really do want to soft kyc you either with a kyc payment method, a phone number, or an IP address. 

 glowie says what?

"hello fellow kids. Proton is surely a CIA honeypot amirite? haha."

nostr:nevent1qqsd0umm0whhzf75f7sx34vm9uzpscn368lz24wkfxpxtr9pzqt9jeqpr3mhxue69uhkummnw3ezucnfw33k76twv4ezuum0vd5kzmqzyqsc8628tpyp6rcjf77e83tve2j9ulj5tnht34fgfrucy5l5j7uh2qcyqqqqqqgs3c2fd 

 I don’t know on which basis but McAfee said Proton was compromised.