[jsheard]

What about the third parties that Reddit has already sold the data to? Does GDPR require Reddit to chase them down and make them delete it as well?

[londons_explore]

yes, and if they cannot, they are violating the GDPR and have to pay fines.

This is why datasets are rarely sold as massive CSV's in the modern world - instead companies with data sell access to API's, with the expectation you'll query for what you need in real time.