[M2Ys4U]

It's personal data. Which is defined in the GDPR as:

any information relating to an identified or identifiable natural person (‘data subject’); an identifiable natural person is one who can be identified, directly or indirectly, in particular by reference to an identifier such as a name, an identification number, location data, an online identifier or to one or more factors specific to the physical, physiological, genetic, mental, economic, cultural or social identity of that natural person

[lukejduncan]

I’m sure the true answer is ambiguous, but “personal data” by that definition seems to imply almost any form of account creation. For sure, that seems to imply you can’t use email addresses as identifiers. Maybe it implies that so long as the data isn’t de facto joinable with side data (phone numbers, email addresses) it may be ok.