Windows has previously been ruled to have a monopoly market share in both the US and the EU.

There's certainly a case that can be made that having Windows licencing fees be many times more expensive (unless you use Microsoft's own cloud service) would be an instance of illegal tying.

> Antitrust concerns arise when such arrangements are used to maintain or augment the seller’s pre-existing market power or impair competition on the merits in the market for the tied product

https://www.law.cornell.edu/wex/tying_arrangement