A startup should not work where there is no market. You should take dissatisfied customers from an existing market, make them yours, and then expand.
Problem interviews are a very simple way to find out what consumers are unhappy with. But not the simplest.
The simplest is reviews. Go and open reviews of your competitor's product. Maps, forums, review services, etc. Collect a large amount of data and immediately understand not only the pain points, but also the wording people use to describe them.