Win32_OperatingSystem lives in root\cimv2 . If your OMI client doesn’t specify the namespace, you’ll see no results.
You can test the OMI connection directly from your collector’s CLI using the tool to rule out console interface issues: win32-operatingsystem result not found via omi
session.query("SELECT * FROM Win32_OperatingSystem") Win32_OperatingSystem lives in root\cimv2