Tom Möller has written a tutorial in the German Joomla forum on how to customize the default Joomla contact form to comply with the GDPR. You can add an extra field to have the visitor confirm the privacy policy.
Why do I need the field in the contact form?
If you collect personal data on your website, e.g. through a contact form or a newsletter subscription, you must inform those affected whether you pass on the data to someone else, where and how long you save them, how they are transferred to you, ...
