get_post_custom_values( string $key = '', int $post_id )

Source

File: wp-includes/post.php

function get_post_custom_values( $key = '', $post_id = 0 ) {
	if ( ! $key ) {
		return null;
	}

	$custom = get_post_custom( $post_id );

	return isset( $custom[ $key ] ) ? $custom[ $key ] : null;
}