Prevent hidden WooCommerce products from showing search results / prevent purchase

functions.php

<?php
/**
 * Add a noindex, follow robots meta tag to hidden products.
 *
 * @param string $robots The robots meta tag.
 * @return string
 */
add_filter(
	'wpseo_robots',
	function ( $robots ) {
		if ( ! is_singular( 'product' ) || ! function_exists( 'wc_get_product' ) ) {
			return $robots;
		}

		$product = wc_get_product();

		if ( ! $product ) {
			return $robots;
		}

		if ( 'hidden' !== $product->get_catalog_visibility() ) {
			return $robots;
		}

		return 'noindex, follow';
	}
);

/**
 * Remove the add to cart button for hidden products.
 *
 * @param bool $purchasable Whether the product is purchasable.
 * @param WC_Product $product The product object.
 * @return bool
 */
add_filter(
	'woocommerce_is_purchasable',
	function ( $purchasable, $product ) {
		if ( 'hidden' === $product->get_catalog_visibility() && ! current_user_can( 'manage_woocommerce' ) ) {
			return false;
		}

		return $purchasable;
	},
	10,
	2
);