Source

File: wp-includes/post.php

function get_lastpostdate( $timezone = 'server', $post_type = 'any' ) {
	$lastpostdate = _get_last_post_time( $timezone, 'date', $post_type );

	/**
	 * Filters the most recent time that a post on the site was published.
	 *
	 * @since 2.3.0
	 * @since 5.5.0 Added the `$post_type` parameter.
	 *
	 * @param string|false $lastpostdate The most recent time that a post was published,
	 *                                   in 'Y-m-d H:i:s' format. False on failure.
	 * @param string       $timezone     Location to use for getting the post published date.
	 *                                   See get_lastpostdate() for accepted `$timezone` values.
	 * @param string       $post_type    The post type to check.
	 */
	return apply_filters( 'get_lastpostdate', $lastpostdate, $timezone, $post_type );
}