I noticed that Whonix wiki is mentioning protonmail.com as suitable mail provider several times. This could be misunderstood as recommendation.
And because it was mentioned in whonix wiki, i also tried to create an account at protonmail.com while using Tor.
But the problem is, that it is not possible to create an account at protonmail.com by using Tor.
If you try to do so, protonmail asks the user for a phonenumber (to send an SMS) or money (which requires a creditcard or similar).
Both options will de-anonymize the user and its email account he wants to use.
Thus this mail provider is not an option for usage via Tor.
It’s also not possible to just try to use some of these free SMS receive providers, because protonmail will bound the provided phone number to the mail account and when it is already in use, which is typically the case for such free disposal phone numbers from these free SMS receive providers, then protonmail rejects to accept the provided phone number. In consequence it’s not possible to create an account without de-anonymization by using Tor.
I would suggest to remove all entries that mention protonmail from the wiki.