> Would you still build that app, because it solves an annoying real world problem even if you got paid $0?
Assuming you’re talking about building an app for other people, I personally would not, no. The market is sending a clear signal that it values the app at zero dollars. In other words, they don’t want it.
> If not then the problem you are solving is probably not important and a waste of your time anyway.
This is exactly the question that charging money answers: Do people just say they want your app or are they willing to “put their money where their mouth is” and actually buy it?
(Also note that not all things are paid for with money. Some are paid for with time or attention, so adjust for that if necessary.)