Building an app addressing a need no other app has ever addressed is a great competitive advantage. Your app can become the top result for the corresponding keywords and the more it’s the top result, the harder it is to beat your app.
Your best shot at finding a novel idea with no competition is to draw on your personal experience outside the tech ecosystem. I built TextingStory because I needed a text message video for a theater play I was creating. There was no existing tool to do what I wanted.
Take inspiration from your other hobbies or interests. It will maximize your chances of finding an app concept that hasn’t already been explored.
Trust your instincts. If you feel an app can be successful, build it. Nobody around me really understood the concept and appeal of TextingStory when I was building it. The app stores have billions of users and you only need a tiny fraction of those to like your app. It turns out nobody around me understood because users weren’t my age or were in different lines of work!