"Assume I don't know anything. Teach me something in the next two minutes about a topic you are passionate about - can be anything". This questions helps me understand how a person thinks on their feet, does storytelling, and uncover more about their passions as a human, that may have some interesting overlap with product work.
I have learned how to swing a gold club, calm down crying toddlers, and pick soil for any plant from asking this question.
For me the biggest differentiator is having a growth mindset. This doesn't just mean they want to make an impact and improve as a PM. For me it comes down to three things: