HIde a single post ID from 'Recent Posts' widget

I have a single post that I dont want showing up in 'Recent Posts' widget
as this post should only be accessible via an offsite link.
https://prnt.sc/10iswqv

I found this as a possible solution which I added to Elements > Hooks > but it does not work
https://prnt.sc/10iszcc

function exclude_single_posts_home($query) {
if ($query->is_home() && $query->is_main_query() && !is_admin()) {
$query->set('post__not_in', array(16461));
}
}

add_action('pre_get_posts', 'exclude_single_posts_home');

any suggestions