But this is exactly the kind of behaviour targeted by the DMA. Artificial restrictions in the functionality of iphone are inserted to drive sales of an unrelated product. It's page one of the Monopolist Playbook.
Maintaining a developer toolkit for Windows and Linux is a major hurdle.
If they intentionally prevent a third party Xcode-compatible implementation from existing, that’s monopolistic behavior. If they don’t want to provide it themselves, it’s a rightful business choice and theirs to make, in my book.