A backlog you shaped, not just maintained
Hiring teams for product owners want to see that you made the backlog say something. Anyone can list that they “managed the backlog”. What separates candidates is evidence that you decided what went in, what stayed out and in what order, and that you can explain why. In the letter, describe one backlog decision: the competing items, the information you used to rank them, and what the team delivered as a result. If you split a large epic into slices that could ship independently, say so, because that is the daily craft of the role.