What personal data is being processed by a Lemmy instance, what are they processing that's being sold in the EU? The GDPR does not apply here, stop trying to wiggle it into something it's not.
Usernames at the very least, as online identifiers.
Art. 4 GDPR Definitions
For the purposes of this Regulation:
‘personal data’ means 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;
And they don't need to be sold, just retained. GDPR applies even if there is no payment anywhere, even to non-commercial entities.
Usernames are not PII...the GDPR only applies if someone is making money from the service. It does not mean just because your site is free but hosts ads or sells user data it's exempt. Lemmy instances do none of this.
What do you think an online identifier is then? And why would the GDPR only apply if there is money made? It specifically says in multiple places free services also count.
How is IBM authoritative on this subject? And even so, this article doesn't say that usernames are not PII, it even indirectly says it is indirect PII.