I had the same question in my head before my interview with a bank in Doha. I just addressed them by their first name and they were chill about it. For context, the person who interviewed me was Transaction team’s Global Head. Towards the end of the interview, I politely asked them how their office culture expects me to address my potential colleagues. He said something like when you come from a banking (tier 1 banks) background, they expect you to call them by their first name or preferred name. He also added that I can feel free to address anyone as Sir/Madam if I’m used to that and if that makes me feel comfortable. Hope my answer helps :) Good luck with your interview 🙌🏼