It's not PII (an American term) but it is personal data (a GDPR term). Personal data is (broadly) considered to be data that could be used to track or tie your

It's not PII (an American term) but it is personal data (a GDPR term). Personal data is (broadly) considered to be data that could be used to track or tie your behavior online together into a profile. The UK's ICO calls out usernames specifically as an example of such data. 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/#:~:text=The%20username%20is%20personal%20data,'real%20world'%20named%20individual https://ico.org.uk/for-organisations/uk-gdpr-guidance-and-re.... (For those of us who have been around on the Internet long enough to remember the era where people intentionally chose handles to remain pseudonymous and separate from their IRL personas, this seems counter-intuitive and a little preposterous, but the GDPR doesn't care what "netizens" think about privacy; it's a broad attempt to impose a "non-native" concept of privacy over the preexisting net culture).