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I'm not sure what you're talking about. Their bootloader explicitly supports other OSes. They make it easy to run Windows (even through a built-in app that helps you set it up). There are plenty of reasons to criticize Apple, but they literally don't do anything to prevent you from running another OS.
Apple Silicon cannot boot Windows ARM and Apple is dropping boot camp support alongside x86 support in the near future.
That's totally up to Microsoft… they could done a licensing deal with Apple years ago to enable Windows ARM to run natively on Apple Silicon hardware.