If Microsoft wanted to be monopolistic, and it wouldn't be the first time, then why are they abandoning their strongest exclusives (Windows, Office) and instead enter a more competitive market, where Google, Amazon, etc... are well established and with no sign of letting go.

Given Office 365 and day-one Game Pass release of all first-party titles, I don't think you need a tinfoil hat to imagine this.

I suspect lingering antitrust concerns are one of the few things standing in the way of locking consumer Windows updates behind a paywall, possibly alongside a "free with ads" version.