In the contact settings, you can set the retention period for the contacts based on which country they are from.

This can be either unlimited or a period amount.

To assist you it is shown if a country enforces GDPR rules.

If a country from which the contact enforces GDPR rules the default is either your default retention setting if it is not unlimited or 26 months.

After the retention period is over the GDPR affected fields of a lead are removed

A contact is forgotten if the last inbound lead from it has been older then the retention period.