I asked for more context. Is this a new or existing app? They said existing. So I asked what was driving the need for change and what are the metrics to prove the need for this change? Then I designed from there. I identified the TAM, and the funnel where they lost users along the way and changed the UX and suggested AB testing to prove it reduced dropoff rates. No idea how I did. The interviewer had an excellent poker face. Maybe they wanted a designer's approach as opposed to PM...but this was a PM interview so I took that angle.