I think there is a huge variance. Some (probably most, tbh) apps see no traction at all, some grow slowly, some take off. But the takeoff can also happen after a long period of slow growth/stagnation, depending on influencers covering it, word-of-mouth, etc. The market is flooded with apps, so you need to think about what you can build that is worth choosing over all of the other options which already exist.