How do I display serialized 'REST Export' with date format rather than timestamp?
Even with the rows being displayed as entities, you can have a hook_views_pre_render(&amp;$views) invocation alter the entity field properties before they are used they are rendered out. 

function MYMODULE_views_pre_render($view) {

  // Only alter my_view_machine_id view, rest_export display
  if ($view-&gt;id() == 'my_view_machine_id' &amp;&amp; 
      $view-&gt;getDisplay()-&gt;definition['id'] == 'rest_export') {
    foreach ($view-&gt;result as $row) {
      if (isset($row-&gt;_entity-&gt;created)) {
        // Alter the entity created property to a readable ISO8601 date
        $row-&gt;_entity-&gt;created-&gt;setValue(date('c', $row-&gt;_entity-&gt;created-&gt;value));
      }
    }
  }
}


There might be a better part of Views rendering pipeline (e.g. REST views export has some templating system) to place this in, but it still renders out the altered serialized property.