exclude posts within the hidden-posts options array

functions.php

<?php

/*
Code references:
  Exclude Posts:
  https://jetpack.me/support/customize-related-posts/#exclude
	
  Hidden posts plugin to grab post list to exclude:
  https://vip-svn.wordpress.com/plugins/hidden-posts/hidden-posts.php
*/


function tt_exclude_related_post( $exclude_post_ids, $post_id ) {
    // $post_id is the post we are currently getting related posts for
    $hidden_posts = array_filter( array_map( 'absint', get_option( 'hidden-posts', array() ) ) );

    if( !empty( $hidden_posts ) ) {
    	$exclude_post_ids = array_unique( array_merge( $exclude_post_ids, $hidden_posts ) );
    }
    
    return $exclude_post_ids;
}

add_filter( 'jetpack_relatedposts_filter_exclude_post_ids', 'tt_exclude_related_post', 20, 2 );