Legally, you can run macOS anywhere you want. Apple cannot and has not stopped anyone from doing that. There is no court of law anywhere which will prevent an end-user from doing what they want with macOS.

However, you most certainly are paying for the OS whenever you buy Apple's overpriced hardware. Perhaps the receipt does not state this fact, but we all know that the only way anyone will get macOS is if someone gives Apple money. So, the people giving Apple money are all paying for macOS... And if you're one of those people, you've paid for macOS.

Saying that you're not paying for the OS is like saying that you're not paying for solar panels when you sign a 15 year deal with some energy company middle-man. It's like saying that you're not paying the full price of a smartphone when you buy it subsidized from the phone carrier. You actually end up paying more for the solar panels and the smart phone in those cases. In this case, you're most likely paying more for the OS as well.

If you want to play games with semantics, anything you want can be true.