No, check GDPR Article 4 (1): personal data means any information relating to an identified or identifiable person.
The content of a post is not personal data (in general) but the things like user name etc are. The content is not relating to an identifiable person (in general) while the user name is.
The content of a post is not personal data (in general) but the things like user name etc are. The content is not relating to an identifiable person (in general) while the user name is.
Shakespeare's poems are not personal data.