How to manage stock for product option SKU's and add-ons
Most types of extra product option are standalone, and do not integrate with the WooCommerce stock management system. They also don't have their own SKU. However, you can create product add-ons with SKU codes and stock control by using the Products option type in the WooCommerce Product Options plugin.
The 'Products' option type lets you select other products or categories to appear on a product, instead of adding the options manually.
Imagine that you're selling a smartphone and want to upsell a case and screen protector on the smartphone product page. The case and screen protector are already available as separate products in your store, and you want their stock levels to update when customers buy them with the smartphone product.
The solution is to use the 'Products' option type to select the case and screen protector so that they appear as options on the smartphone product. That way, customers can add all three products to their cart at once, and the stock of each product will update correctly. That way, they are product add-ons with SKU's and stock, just like any other WooCommerce product.