wpseo_robots does not working correctly

Hello everyone, I’m just faced issue when trying to remove noindex from search page on my wordpress site.

I’m using wordpress 6.0.3 and yoast 19.13

add_filter('wpseo_robots', 'yoast_no_home_noindex', 999);

function yoast_no_home_noindex($string) {
    $string = "";
    if (is_home() || is_front_page() || is_search()) {
        $string= "index,follow";
    }
    return $string;
}

I am using this code to remove the noindex, follow. But instead it is adding the content.

<meta name="robots" content="noindex, follow, index,follow">