Drupal 8: Prevent webform from saving IP
You could override the save function of webform/src/WebformSubmissionForm.php, but as you specifically ask for a hook and because this is probably also the easiest solution you can remove the field value set by the form before the entity gets saved:

use Drupal\webform\WebformSubmissionInterface;

/**
 * Implements hook_ENTITY_TYPE_presave() for webform submissions.
 */
function mymodule_webform_submission_presave(WebformSubmissionInterface $webform_submission) {
  $webform_submission-&gt;remote_addr-&gt;value = '';
}