Exclude pages that have been noindex-ed in Yoast SEO from WP search

functions.php

<?php // Do not copy this line

add_filter( 'pre_get_posts', 'dw_exclude_noindex_content_from_search' );

function dw_exclude_noindex_content_from_search($query) {

	// Only run this query for searches when not inside the admin	
	if ( $query->is_search && !is_admin() ) {
		
		// Find all posts with `_yoast_wpseo_meta-robots-noindex` postmeta that equal to `1`
		$args = array(
			'post_type'   => 'any',
			'posts_per_page'=> -1,
			'post_status' => 'publish',
			'meta_query' => array(
		        array(
		            'key'     => '_yoast_wpseo_meta-robots-noindex',
		            'value'   => '1',
		        ),
		    )
		);
		$exclude_query = new WP_Query( $args );
		
		// Create array of post IDs only
		$exclude_posts_array = array();
		
		// Fill the array
		if ( $exclude_query->have_posts() ) {
			while ( $exclude_query->have_posts() ) {
				$exclude_query->the_post();
				$exclude_posts_array[] = get_the_id();
			}
		} 
		
		// Reset the query
		wp_reset_postdata();
		
		// Modify the search query to exclude the noindex-ed content
		$query->set( 'post__not_in', $exclude_posts_array ); 

	}

    return $query;
    
}