functions.php

<?php

/**
 * Remove produtos fora de estoque do cross sell
 * @See https://github.com/woocommerce/woocommerce/blob/444dffdda27750b98ce1517d5f6f4d8153c53967/includes/class-wc-cart.php#L817
 */
add_filter('woocommerce_cart_crosssell_ids', 'remove_out_of_stock_from_crosssell', 10, 1 );
function remove_out_of_stock_from_crosssell( $wp_parse_id_list ){
	if (!empty($wp_parse_id_list)) {
		foreach ($wp_parse_id_list as $product_id) {
			$product = wc_get_product($product_id);

			// Verifica de o produto esta fora de estoque
			if ( $product->managing_stock() && !$product->is_in_stock() ) {
				
				// Remove o produto da listagem
				if (($key = array_search($product_id, $wp_parse_id_list)) !== false) {
					unset($wp_parse_id_list[$key]);
				}
			}
		}
	}

	return $wp_parse_id_list;
}