During the very early days of Android (2010, I think) I made some terrible arcade games. They made about 100$ a month from ads and I sold the rights for distribution in Korea for 600$ a game to a company that no longer exists (ubi-nuri). Live wallpapers became a thing at some point, and I sold some procedure generated garbage for $0.99. I think I made somewhere between 3-4k GBP out of the whole thing.

Then the market got very competitive, the "recently updated" section was removed and everything died immediately for me. I have no idea how you would get users now without an advertising budget.