How to pass a Date as Contextual Filter?
Finally, I made it work.
I used mymodule_views_query_alter replacing the operator of the proper condition:  

  if ($view-&gt;id() == 'services' &amp;&amp; $view-&gt;current_display == 'embed_2') {
    foreach ($query-&gt;where as &amp;$condition_group) {
      foreach ($condition_group['conditions'] as &amp;$condition) {
        if ($condition['field'] == 'service.additiondate') {
          $condition['operator'] ='&gt;=';
        }
      }
    }
  }