aceca

Usernames are online identifiers:

https://ico.org.uk/for-organisations/uk-gdpr-guidance-and-resources/personal-information-what-is-it/what-is-personal-data/what-are-identifiers-and-related-factors/

A non-exhaustive list is included in Recital 30

An individual’s social media ‘handle’ or username, which may seem anonymous or nonsensical, is still sufficient to identify them as it uniquely identifies that individual. The username is personal data if it distinguishes one individual from another regardless of whether it is possible to link the ‘online’ identity with a ‘real world’ named individual.

If a user is commenting they have an online identifier and are thus covered. If a user has ever referenced their relationship status, location or any physical descriptor they are covered. The GDPR – it applies.