Windows source isn't all that hard to see. I know they've made it available to some universities and large customers also can get access.
https://www.microsoft.com/en-us/sharedsource/enterprise-sour...
https://www.microsoft.com/en-us/sharedsource/enterprise-sour...
And, IIRC, infamously the Chinese government too, because they made it a pre-condition of them purchasing Microsoft licenses that they must have source code visibility.
Even the communist party in China is more up to date then my own government
Well, there is for sure a lot to criticize about the CN government, but this precondition seems to me very natural (the OS is a very natural place for possible backdoors, otherwise...)