Smartphones are in a market, yes...? I can also buy an Android or Pinephone, or use an open source OS like Graphene. That means you have a choice not to use iPhone's garden or use Google's or none... via F-Droid style app stores.

Do you think free-markets means corporations also need to run their business operations and products/platforms like a market? Because that's not what that means. (Even if it did ideological purity is dumb)

Inversely governments forcing companies to all operate with the same business model is not on a free market.

The only thing that would prevent a walled garden from operating in a free market is if Apple et al was a monopoly/oligopoly and you had no other choices. I've already said antitrust laws for things like browser choice is one of the better solutions than the one proposed.

this is a non-sequetor: just because Smartphones and Shoes are a free market has no relevance of whether Apps are a free market. A has no effect on B.

If you want to sell an app, you have to deal with rules of App Store or Play Store, or Windows Store. You can't even sell pornographic apps - this is the definition of an unfree market.