GDPR is focused on PII and anything that can identify you directly or indirectly as an individual.

If your posts start with “My name is Jane Doe and this is my post” then that would be one thing.

However from everything I’ve been able to ascertain, your average forum post is unlikely to be covered, save from anonymizing the email address etc.

Granted there are certain things that can lead to deanonymization, in the case of forum posts I’m unsure how far that goes.

It’s a myth that the GDOR “right to be forgotten” is an absolute.

I also suspect that creating anonymized IDs and attributing that ID to each thread would be enough to get past such attempts to link posts to PII.