Add Last Modified Column

add_filter( 'manage_posts_columns', function ( $columns ) {

	$columns['last_modified'] = __( 'Last Modified' );

	return $columns;

} );

add_action( 'manage_posts_custom_column', function ( $column, $post_id ) {

	if ( 'last_modified' === $column ) {

		$modified_time = get_the_modified_time( 'Y/m/d g:i:s a', $post_id );

		echo esc_html( $modified_time );

	}

}, 10, 2 );