I develop a basketball coaching app called Elite Hoops, it makes $3.5k/month and thankfully growing:

--> https://elitehoopsapp.com

I wrote a book series over iOS development, self-published, made over $120k:

--> https://bestinclassiosapp.com

I do one sponsored ad a year, which translates to over $500/month (i.e. your criteria):

--> https://www.swiftjectivec.com

And launching another app soon to follow D2/D3 collegiate scores, hoping to get that up and over $500 MRR quickly:

--> https://x.com/JordanMorgan10/status/1864796895396110737