Not quite. Because that requires pushing an update and only hits those who have windows automatic updates enabled. A lot of companies run those updates on a slight delay, which means they have a decent enough window to block such an update. Microsoft is a big thing to worry about when it comes to independence from the emerging fascist government of the US. But not because 'they can shut off windows'.

The short-term fear should be in enterprise cloud (See ICC judges). The long-term pain lies in blocking security updates (As happened to Russia). One might worry about malicious updates being pushed, but the legal grounds for that are flimsy to non-existent, and Microsoft has very strong business reasons to push back. So even the trump administration would be smart enough to instead target the cloud solutions. Since the legal precedent is very clear and well lubricated "providing services to sanctioned entities", and the business impact is equally crippling.