Webflow has variants but not add ons.
this might be worth a shot, but I don’t have a live e-commerce site to test if this works at checkout on a product page.
It might be worth trying to create a multi-reference “Add on” field in products self referencing the Product table. Then on the product page add a product collection and filter it for the current product. It will show only available add ons for that product. But yeah I am not sure the ad to cart code can handle this multiple instances.