Enable sorting in views format settings. The column header becomes clickable but throws the following error:
Drupal\Core\Database\DatabaseExceptionWrapper: Exception in Admin Content[content]: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'unknown' in 'order clause': SELECT "node_field_data"."nid" AS "nid", "users_field_data_node_field_data"."uid" AS "users_field_data_node_field_data_uid" FROM {node_field_data} "node_field_data" INNER JOIN {users_field_data} "users_field_data_node_field_data" ON node_field_data.uid = users_field_data_node_field_data.uid WHERE (node_field_data.status = 1 OR (node_field_data.uid = 5 AND 5 <> 0 AND 1 = 1) OR 1 = 1 OR 1 = 1) ORDER BY "unknown" ASC LIMIT 50 OFFSET 0; Array ( ) in Drupal\views\Plugin\views\query\Sql->execute() (line 1548 of core\modules\views\src\Plugin\views\query\Sql.php).