How do I tailor a demo to a buyer's real problem?

You can show the product. Tailoring the demo to a buyer's real problem is the harder skill, and it is the one that actually sells. A generic walkthrough shows what the product does. A tailored one shows this person how their specific pain goes away, and those land completely differently. The reason it eludes you is probably that you are leading with features instead of their problem. You know the product so well that you want to show all of it. But the buyer does not care about all of it. They care about the two or three things that touch what keeps them up at night, and the rest is noise to them. So do the work before the demo, not during it. Find out what this buyer's real problem is, and then build the demo around solving that, cutting everything that does not speak to it. Even one good discovery question ahead of time changes the whole thing. You are not showing a product. You are showing one person their own problem, solved. Aim there and the demo starts to sell itself.