Unfortunately, adding these optional fields to our current JSON-LD setup is not possible at the moment.

Adding return policy and shipping details into our structured data poses significant challenges, primarily due to the unavailability of such features in Shopify and more complexity arises as shipping information can vary based on the customer's location.

As the fields are optional, you can currently disregard the warning. Everything will function as intended.

Read official Shopify answer here: https://community.shopify.com/c/shopify-design/how-do-i-add-quot-hasmerchantreturnpolicy-quot-and-quot/m-p/2041438#M542732