Your question is Measuring UX Design Success. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How would you measure whether a new UX design for a media product is successful?
Explain how you would translate the design goal into a primary KPI, supporting engagement and conversion metrics, and guardrails. Describe the data, comparison method, and timeframe you would use to determine whether the design caused meaningful improvement.