Hi,
I didn't find any official doc mentioned the "OperatingSystem" and "OperatingSystemVersion" attributes. Just to be on the safe side, it is recommended not to modify it manually. Have you run Update-ClusterFunctionLevel after upgrading all the nodes to Windows Server 2016? If not, you can run it from powershell and see if those attributes are updated.
Best Regards,
Ian Xue
If the Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.