Which is like saying that Subaru is dominant in the market for new cars sold at Subaru dealerships.
That completely ignores the fact that there is intense competition for developers and users between Android and iOS, and renders the point moot.
Sure, you can always define an arbitrary market for which a company will have dominance, but that's irrelevant from an economics perspective.
Maybe you should go read on what a monopoly actually is...
Here's a good interview with the economist who taught me what a monopoly is:
https://hbr.org/2017/11/as-more-people-worry-about-monopolie...
Will be a good point for you to start.