A second approach is to travel. You'd be surprised how different things are in other countries. I got the idea of selling coffee from Australia, where great coffee is common and Starbucks was "tourist level". Australia also has a lot of mental health apps, which I'm working on now.
My first app was also heavily localised for non-urban Malaysians. There are plenty of keto recipe alternatives for Western food e.g. bacon and eggs. But Malaysia it's a lot harder because the culture is heavily rice based, so a keto recipe app is much more valuable.
So, you can also do subsets of a problem. Like Facebook and Harvard, Amazon and books, Apple and MP3 players.