Exclude posts from wordpress search that have the yoast setting for 'allow search engines to index' set to 'no'

functions.php

<?php
// add the below code to your child theme functions file

// exclude yoast noindex pages from wp search
function exclude_noindex_from_search( $query ) {
    if(is_admin() || !$query->is_main_query()) {
        return;
    }
    if($query->is_search) {
        $meta_query = array(
            'relation' => 'OR',
            array(
                'key'     => '_yoast_wpseo_meta-robots-noindex',
                'compare' => 'NOT EXISTS',
            ),
            array(
                'key'     => '_yoast_wpseo_meta-robots-noindex',
                'value'   => '1',
                'compare' => '!=',
            ),
        );
        $query->set('meta_query', $meta_query);
    }
}
add_filter( 'pre_get_posts', 'exclude_noindex_from_search' );