Google added returnPolicyCountry to the return policy code examples within the Google Merchant Center structured data document. This is because Google requires returnPolicyCountry for MerchantReturnPolicy.
Google added a quick note about this update to its doc update page and said, "Added returnPolicyCountry to the return policy examples" because "returnPolicyCountry is required for MerchantReturnPolicy."
Here is a screenshot of what was added to this document based on comparing the live page to the archived page. I highlighted the additional line in orange:
Forum discussion at X.
