[m-p-3]

I have an email that I've created and only accessed through their Tor hidden service hostname

   https://protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/

and I was never asked to provide any personally identifying information.

[flotzam]

As always when people post this, I just tried it with Tor Browser, and, as always: "No verification method available"

Did you access the .onion with something more fingerprintable like Brave?

[m-p-3]

No, just the plain Tor Browser.