function get_feed_build_date( $format ) {
	global $wp_query;

	if ( empty( $wp_query ) || ! $wp_query->have_posts() ) {
		// Fallback to last time any post was modified or published.
		return get_lastpostmodified( 'GMT' );
	}

	// Extract the post modified times from the posts.
	$modified_times = wp_list_pluck( $wp_query->posts, 'post_modified_gmt' );

	// If this is a comment feed, check those objects too.
	if ( $wp_query->is_comment_feed() && $wp_query->comment_count ) {
		// Extract the comment modified times from the comments.
		$comment_times = wp_list_pluck( $wp_query->comments, 'comment_date_gmt' );

		// Add the comment times to the post times for comparison.
		$modified_times = array_merge( $modified_times, $comment_times );
	}

	// Determine the maximum modified time.
	$max_modified_time = mysql2date( $format, max( $modified_times ), false );

	/**
	 * Filters the date the last post or comment in the query was modified.
	 *
	 * @since 5.2.0
	 *
	 * @param string $max_modified_time Date the last post or comment was modified in the query.
	 * @param string $format            The date format requested in get_feed_build_date.
	 */
	return apply_filters( 'get_feed_build_date', $max_modified_time, $format );
}