Add Custom Field Column to Post or CPT Admin

// add featured image thumbnail to admin
// Add the column to admin
function add_featured_image_column ( $columns ) {
   return array_merge ( $columns, array ( 
     'featured_image'   => __ ( 'Featured Image' )
   ) );
}
add_filter ( 'manage_properties_posts_columns', 'add_featured_image_column' );
 
// Add featured image thumbnail to the column
add_action('manage_properties_posts_custom_column', 'display_thumbnail_column', 5, 2);
function display_thumbnail_column($column_name, $post_id){
  switch($column_name){
    case 'featured_image':
      $post_thumbnail_id = get_post_thumbnail_id($post_id);
      if ($post_thumbnail_id) {
        $post_thumbnail_img = wp_get_attachment_image_src( $post_thumbnail_id, 'thumbnail' );
        echo '<img width="80" src="' . $post_thumbnail_img[0] . '" />';
      }
      break;
  }
}

// Move custom column before "title" column
add_filter('manage_properties_posts_columns', 'cb_reorder_columns');
function cb_reorder_columns($columns) {
  $n_columns = array();
  $move = 'featured_image'; // which column to move
  $before = 'title'; // move before this column

  foreach($columns as $key => $value) {
    if ($key==$before){
      $n_columns[$move] = $move;
    }
    $n_columns[$key] = $value;
  }
  return $n_columns;
}