[0]European Commission defines personal data as: >Personal data is any information that relates to an identified or identifiable living individual. Different pieces of information, which collected together can lead to the identification of a particular person, also constitute personal data.

Thus, anything you wrote on any site, if it is not anonymised and still linked or could be traced to your account is a personal data.

And even when it is anonymised: >Personal data that has been de-identified, encrypted or pseudonymised but can be used to re-identify a person remains personal data and falls within the scope of the GDPR.

[0] - https://commission.europa.eu/law/law-topic/data-protection/r...