Restricted product displaying in search results

there are some Plugins that will offer such a function: CatalogX (Freemium) or WooCommerce Catalog Mode
or you might use code snippets – but it is not as easy as it sounds. There are still backdoors that can be used to find something.

but this might give you a chance to exclude some Products by slugs ( f.e.: members-only or premium)

This is what an AI like Claude would give to you:

// 1. Hide from queries
add_action('pre_get_posts', 'hide_member_products_from_guests');
function hide_member_products_from_guests($query) {
    if (is_admin() || !$query->is_main_query()) {
        return;
    }
    
    if (!is_user_logged_in()) {
        $tax_query = $query->get('tax_query') ?: array();
        
        $tax_query[] = array(
            'taxonomy' => 'product_tag',  // product_cat → product_tag
            'field'    => 'slug',
            'terms'    => array('members-only', 'premium'),  // Deine Tag-Slugs
            'operator' => 'NOT IN'
        );
        
        $query->set('tax_query', $tax_query);
    }
}

// 2. Visibility Filter
add_filter('woocommerce_product_is_visible', 'filter_member_products_visibility', 10, 2);
function filter_member_products_visibility($visible, $product_id) {
    if (!is_user_logged_in()) {
        if (has_term('members-only', 'product_tag', $product_id)) {  // product_cat → product_tag
            return false;
        }
    }
    return $visible;
}

// 3. Block direct access
add_action('template_redirect', 'block_member_product_access');
function block_member_product_access() {
    if (!is_user_logged_in() && is_product()) {
        global $post;
        if (has_term('members-only', 'product_tag', $post->ID)) {  // product_cat → product_tag
            wp_redirect(wp_login_url(get_permalink()));
            exit;
        }
    }
}

// 4. Exclude from search (maybe an ajax pendent is needed too)
add_filter('posts_where', 'exclude_member_products_from_search', 10, 2);
function exclude_member_products_from_search($where, $query) {
    global $wpdb;
    
    if (!is_admin() && $query->is_search() && !is_user_logged_in()) {
        $where .= " AND {$wpdb->posts}.ID NOT IN (
            SELECT object_id FROM {$wpdb->term_relationships}
            INNER JOIN {$wpdb->term_taxonomy} ON {$wpdb->term_relationships}.term_taxonomy_id = {$wpdb->term_taxonomy}.term_taxonomy_id
            INNER JOIN {$wpdb->terms} ON {$wpdb->term_taxonomy}.term_id = {$wpdb->terms}.term_id
            WHERE {$wpdb->terms}.slug IN ('members-only', 'premium')  // Deine Tags hier
            AND {$wpdb->term_taxonomy}.taxonomy = 'product_tag'  // product_cat → product_tag
        )";
    }
    
    return $where;
}

// 5. Exclude from REST API 
add_filter('woocommerce_rest_prepare_product_object', 'hide_member_products_from_api', 10, 3);
function hide_member_products_from_api($response, $object, $request) {
    if (!is_user_logged_in() && has_term('members-only', 'product_tag', $object->get_id())) {  // product_cat → product_tag
        return new WP_Error('rest_forbidden', 'Zugriff verweigert', array('status' => 403));
    }
    return $response;
}