yoast_seo_indexables_remove_post_types.php

<?php
/********* DO NOT COPY THE PARTS ABOVE THIS LINE *********/

/* Prevent Yoast SEO for adding specific post types to indexables
 * Credit: Yoast team
 * Last Tested: Jan 18 2021 using Yoast SEO 15.6.2 on WordPress 5.6
 * Documented: https://github.com/Yoast/wordpress-seo/blob/trunk/src/helpers/post-type-helper.php#L90
 * Common post types: 'post', 'page', 'attachment', 'product'
 */

add_filter('wpseo_indexable_excluded_post_types', 'yoast_exclude_some_custom_post_types');

function yoast_exclude_some_custom_post_types ( $excluded_post_types ) {
	$excluded_post_types[] = 'post_type_slug'; // Repeat for each type to exclude
	return $excluded_post_types; // Do not remove this line
}