Got setup a call to talk to the CEO. What questions should I ask him?

Hard to know without more context but the biggest red flags I've seen are around honesty about burn rate and runway (most will tell you at the current burn rate but the current burn rate will be wrong as soon as they hire you... If they are not idiots will have calculated exactly what's the plan before the gas runs out). Product vision, sales execution vision, what's plan b (there's always a plan b but nobody talks about it) and what's their go-to heuristic to make hard decisions. You want to get a sense for that person, he/she is the person in charge of making sure you get a paycheck and some sort of payoff for your work. Make sure they know what they are doing.

Ask him if he's a cross dresser

Ask more detailed operational stuff to evaluate if they can survive. If you ask about vision or differentiation, they can bullshit their way until convincing you. After all, that's what startup CEO's do.

With Startups, don't assume anything because everything depends on the founders whim. How do you evaluate employees? Who was your best employee? How are engineering decisions made? What if I disagree with a technical decision? What is the role of founders? What is the role of upper management? What happens if there is a recession? Have you fired anyone? How do you know your product is a hit? How do you add features to the product? Who is your most productive person on staff and why?

Ask him his TC and YoE😜 On a serious note, ask them about their vision, whether they have pivoted from their original plan/go-to-market strategy, name some of their clients, whenever the company has enough runway in terms of funding, if they plan to have additional funding rounds in near future, how they would define the company culture, what keeps them up at night or worries them most, etc