set the order of the pages in the admin section descending according to the editing date

				
					function orderby_modified_posts( $query ) {
    if( is_admin() and isset($_GET['post_type']) and $_GET['post_type'] === 'page') {
  $query->set( 'orderby', 'modified' );
        $query->set( 'order', 'desc' );
    }
}
add_action( 'pre_get_posts', 'orderby_modified_posts' );