If I’ve got it right it’s anything that can directly or indirectly identify you. I would’ve thought most things here wouldn’t fall under gdpr except maybe email addresses or if they’ve specifically mentioned something identifiable in comments or posts. One other thing I think that might be a problem is the data on pictures from a phones camera might indicate where and when it was taken which could narrow down that users location. I know some hosting sites strip this data but some might keep it.