If you want vba code that can be used all over the office products WMI is one solution.
The thing with Application.System.OperatingSystem that its not returning anything interesting.
Application.System.Version is usable. But I use the WMI to give me the correct information.
Sub test()
Dim info As System
'Well everything is windows NT today..
Debug.Print Application.System.OperatingSystem
'Short version string MajorVersion.MinorVersion
Debug.Print Application.System.Version
Dim objWMI As Object
Dim objSystems As Object
Dim objOs As Object
Set objWMI = GetObject("winmgmts:{impersonationLevel=impersonate}!\\.\root\cimv2")
Set objSystems = objWMI.ExecQuery("Select * from Win32_OperatingSystem")
For Each objOs In objSystems
Debug.Print objOs.Name 'Full name as in OS startup screen
Debug.Print objOs.Caption ' Human readable name
Debug.Print objOs.Version ' the correct windows version string
Next
Set objOs = Nothing
Set objSystems = Nothing
Set objWMI = Nothing
End Sub