Neither Apple’s users, nor developers for iOS are forced to do anything.

Comparing buying a phone to being enslaved is quite bizarre.

This is exactly the perspective we disagree over: in my opinion, Apple users and developers are absolutely forced to do something.

There is a thing. They may or may not prefer different ways of handling that thing. Apple makes a choice for them, and prevents them from making their own choice.

Call it what you will, but in my book, lacking the freedom to make your own choices is the definition of slavery.

Can you explain how anybody is forced to either buy an iPhone, or develop for it?

I am not aware of Apple using force to make people do either of these things.