To offer a modest counterweight here, every iPhone owner bought the product knowing damn well that Apple keeps the OS locked down. If you don’t want that, don’t buy an iPhone. There’s no confusion about what the product is and what you can do with it.
So how is a 3rd party going to give support to a customer with iPhone, if Apple will ban such 3rd party for whatever reason?
Let's say that given 3rd party is making a device, which can be controlled via Bluetooth from Windows, Android, MacOS and iOS. They don't make any money on any applications, but from the device.