Make sure WSUS is fully updated.
Run the WSUS Server Cleanup Wizard to remove unnecessary updates and improve overall performance.
Review your Group Policy settings to ensure they're not forcing Windows 10 update behavior on Windows 11 machines.
Under Group Policy navigate to:
Computer configuration > Administrative Templates > Windows Components > Windows Update > Windows Update for Business > Select the target feature update version.
Set the target version to your desired Windows 11 version.