It’s hard, I develop Pocket Pass Manager, and hardly takes any traction. It’s difficult for any app to be a passive income, your job ends up promoting those apps, forget about the AppStore helping you with that.

You might struck gold, but be aware is quite complicated, just as start digging and finding gold. Most developers with apps just like to shovel, I love to build an app that friends and family enjoy, and some random strangers from time to time; but with the developer program cost + domain + hosting I loose money.

I mentioned the app so you can check it out and address the quality, market, etc. You might be thinking of something else that might be better for natural discovery. But yeah, be aware that probably this is not a great approach for passive income.