My Mac App Store only scanning app (https://www.pdfscannerapp.com/) still makes approximately this much a month after nearly 15 years on the store (I published it on day one when the store was realeased) - all updates since then have been free, so I'm just selling to new customers.
It's a hobby project that keeps me into Apple platform development and allows me to work on it in bursts (like the last update for Liquid Glass) and then let it rest for a while (if Apple doesn't break any APIs).
