The crucially important subtlety here is that Apple requiring developers to use the App Store doesn't leverage an existing monopoly (like what Microsoft had with Windows).

Compare the games console market. Nintendo is allowed to say you have to go through them to sell games for the Switch, ditto Microsoft with the Xbox. Sony doing the same thing with the Playstation is exactly equivalent, but they're approaching the sort of market dominance where it might soon be illegal for them (and them alone) to do that in some markets.

> The crucially important subtlety here is that Apple requiring developers to use the App Store doesn't leverage an existing monopoly (like what Microsoft had with Windows).

Copyright (e.g. over iOS) and patent (e.g. over iPhone hardware) are explicitly government-granted monopolies. Having that monopoly is allowed on purpose, but that isn't the same as it not existing, and having a government-granted monopoly and leveraging into another market are two quite distinct things.

> Compare the games console market.

Okay, all of the consoles that require you to sell you to sell through their stores shouldn't be able to do that either.

> but they're approaching the sort of market dominance where it might soon be illegal for them (and them alone) to do that in some markets.

Wait, your theory is that a console with ~50% market share has market dominance but Apple with ~60% of US phones doesn't?