[immibis]

This is different each time you try it. They may use the exit node's country (I doubt they'd be so naive), some other fingerprinting, or just have a limited number of anonymous accounts to give out each day, which is what cockli does. Sometimes you need a phone number, other times an email address, other times just a CAPTCHA.

[crtasm]

Yes, I just tested it and was able to register by giving a (disposable) email.

It did then prompt me to add an email and/or phone number as recovery methods, but that step was skippable.

[mttpgn]

I have never found protonmail's signup step asking for phone number verification or a recovery email to be unskippable.

Protonmail can still be the best choice for a pseudonymous mail service so long as it's combined with diligent, consistent IP address obfuscation. Protonmail will continue to allow logins and new account creations over Tor. All the major free email providers have long since disallowed new signups over Tor, and most have some form of degraded user experience when logging in over Tor, if they allow it at all. Small, niche email providers appear and disappear so often that relying on them still to exist even a few months into the future is a big gamble. Hosting one's own email requires payment of some type to the hosting provider, so it is not anonymous. Other privacy-oriented free email providers, such as riseup, will do exactly what protonmail did, because if they refuse, their only option is to go the way of lavabit.