Chrome security and Google project zero wrote that windows 7 is insecure, will never get the security fixes in Windows 10 and you shouldn't use it.
I presume Google have not relaxed that rule for Windows 10.
I have been thinking about using OpenBSD - but I am guessing that a secure OS is no help when you need to use insecure apps.
I asked them about this particular rule and they said they were allowed to use Windows but certain other engineers were not allowed to.
I came from the same understanding as you but my new understanding was that except for certain departments they are allowed to use Windows.