The product owner at Cloud Kicks wants to know which user stories fail user acceptance...

This answer states that enabling history in the shared spreadsheet is what the BA should recommend to ensure UAT results are documented securely after receiving verbal acceptance of all user stories by the product owner for developing a new Commerce Cloud implementation at CK. History is a feature that allows users to view, restore, or compare previous versions of a document or a file. Enabling history in the shared spreadsheet means that the BA turns on this feature in the spreadsheet where user stories are stored, such as Google Sheets, Microsoft Excel, etc. Enabling history in the shared spreadsheet is what the BA should recommend to ensure UAT results are documented securely because it helps the BA to track and record who made what changes to user stories and when, and to prevent or recover any accidental or unauthorized changes to user stories. References: https://trailhead.salesforce.com/en/content/learn/modules/salesforce-business-analyst-quick-look/use-stakeholder-engagement-skills