hi there, we’re happy to speak to this. Unfortunately, we had to restrict access to our service for protonmail (and a few other email providers) some time ago (more than two years - it is not a recent change)
We found that, when we allow protonmail email addresses on our system, we experience an extreme uptick in accounts with spam, fraudulent activity, phishing, illegal (by US law) pornography, dmca violations, and things of that nature. The extent was so severe that our paying customers, search engine results, and legitimate business side of things were being negatively impacted. We understand that blocking an entire email provider is quite drastic, but it was the only way to mitigate the impact on our service.
I don’t have information on hand at this second as to which email providers are on our list of frequently abused services, so you might find that one of those providers you listed does work, but unfortunately protonmail does not and likely will not be unbanned as the security risk is simply too great.
I wish I had better news for you! If you have follow up q’s, I’d be happy to try and answer them.