That is a huge claim, thrown around by you with no backing. You could get a few economists to discuss that for ages without reaching a conclusion.
Unless you're talking about the layman's definition of monopoly, which means "whatever I want it to mean".
This is particularly relevant when there's the Amazon app store, and app preloads, and the Korean app store, and Fortnite isn't available on the Play store.
And that's before we get into the fact that iOS competes with Android, and that includes the app stores. This would be like complaining that to get a product to be sold by Walmart, you need to get Walmart to sell it.
No matter how you look at it, consumers never had so many choices, prices have never been this low, and app distribution has never been so easy.