This piece of code excludes posts from the WordPress search which have the robots meta settings on noindex, following the Yoast SEO settings.

exclude-noindex-posts-from-search.php

<?php

add_action( 'pre_get_posts', function( \WP_Query $query ) {
	if( ! is_admin() && $query->is_main_query() && $query->is_search() ) {
		$meta_query = [
			'relation' => 'OR',
			[
				'key' =>  '_yoast_wpseo_meta-robots-noindex',
				'value' => '1',
				'compare' => '!=',
			],
			[
				'key' =>  '_yoast_wpseo_meta-robots-noindex',
				'value' => '',
				'compare' => 'NOT EXISTS',
			]
		];

		$query->set( 'meta_query', $meta_query );
	}

	return $query;
});