Unindexing/removing/excluding certain posts programitcally via php hooks

Hello

I have the following Post Type/Taxonomy setup:

Post type: “Grants”
– Custom Taxonomy: “Person”
– Custom Taxonomy: “Program”
— Taxonomy term for this example “Youth Service Improvement Grants”
Post Type: “People”

The “Person” taxonomy creates a relationship between the custom post type “People”– the “Person” terms correspond one to one (they share the same slug) with a “People” post.

What I want to do is *exclude* certain People posts from displaying in the search filter pro results page. The logic for exclusion is:

If a Person tax term is only used on Grants with the “Program” taxonomy term called “Youth Service Improvement Grants” then find the corresponding “People” post and **exclude** that post from the search filter pro results page.

I’ve tried doing this via the WordPress pre_get_posts hook, but it is not working. After adding this code I try rebuilding the index cache via the Search Filter admin panel and refreshing the front-end.

How can I exclude certain posts from being indexed?

Pre get posts:

	add_action('pre_get_posts', 'exclude_people', 10);
	function exclude_people($query){

	    if(!is_admin() && $query->is_main_query() && $query->is_search) :
			$posts_to_exclude = array();
			
			$args = array(
				'posts_per_page' => -1,
				'post_type' => 'grants',
				'tax_query' => array(
				    array(
				      'taxonomy' => 'program',
				      'field' => 'slug',
				      'terms' => array('youth-service-improvement-grants'),
				    ),
				),
			);
			
			$myposts = get_posts( $args );
			foreach ( $myposts as $post ) : setup_postdata( $post );
				$tags = get_the_terms($post->ID, 'person');
				
				if(!empty($tags)) {
					
					
					foreach($tags as $tag) {
						$tag_slug = $tag->slug;
						$tag_terms = array($tag_slug);
	
						$args = array(
							'posts_per_page' => -1,
							'post_type' => 'grants',
							'tax_query' => array(
								'relation' => 'AND',
							    array(
							      'taxonomy' => 'person',
							      'field' => 'slug',
							      'terms' => $tag_terms
							    ),
		                        array(
							        'taxonomy' => 'program',
							        'field'    => 'slug',
				      				'terms' => array('youth-service-improvement-grants'),
				      				'operator' => 'NOT IN'
		                        ),
							)
						);
						
						$my_person_posts = get_posts( $args );
						
						if(count($my_person_posts) < 1) {
							
							$myperson = get_page_by_path( $tag_slug, OBJECT, 'people' );
							
							if(!empty($myperson)) {
								$posts_to_exclude[] = $myperson->ID;
							}
						}
					}
				}
			endforeach; 
			wp_reset_postdata();

	        $query->set('exact', true);
	        $query->set('post__not_in', $posts_to_exclude);
	    endif;
	}