Microsoft had extensive documentation of nearly every API they support, and some they don't. Comprehensive documentation with notes and caveats. Automatically available from their tools.
Compare, for instance, with Apples almost total non-documentation of anything. Mostly just scraped comments with arguments barely described e.g 'a string'. No notes, no architecture, nothing.
Interesting, I've never found Microsoft documentation for Windows thorough enough to reason about a problem, especially when compared to Arch or Gentoo's docs. I always feel like I'm reading the abstract of a paper, with no access to the rest of it. Is there some kind of special access or login requirement for deeper documentation, or am I just spoiled by the great Linux docs?
Apple products are the king of the "you don't own your device" mantra. I just refuse to develop anything for them, because the time expense of trying to guess how to get the OS to comply hasn't been worth the reward. That being said, I've found the documentation for Swift to be extremely good, better than most other languages I work with.
I was privileged(?) to have access to source under license for years, contracting with a company that ported Windows to various industrial platforms. So my view is similarly colored.
Linux is definitely the king, no argument there.