For this question, I'd highly recommend choosing any topic that genuinely interests you/you can passionately write about. If that happens to be a commercial/legal topic, then great - but it also doesn't have to be.
Personally, the answers to this question that have stood out to me the most have been on topics that candidates were personally interested in outside of the domain of commercial law or mainstream areas like Brexit/legal tech (which would come up over and over again).
I would also highly recommend this thread from
@Hazal:
https://www.thecorporatelawacademy....ing-tip-2-discussing-commercial-stories.1280/. Back in the day, she wrote about Netflix for this question and it remains one of the strongest answers I've read!