@Richard Long,Thanks for posting in Q&A.
From your description, I know you want to create a dynamic group for only Intune enrolled Windows devices but exclude servers.
For the built in Dynamic group rule, based on my checking, I find there's no attribute to distinguish windows client and server.
But maybe we can assign device categories to windows 10/11 devices and then create Dynamic group according the deviceCategory.
https://learn.microsoft.com/en-us/mem/intune/enrollment/device-group-mapping
Meanwhile, based as I know, windows serve can't enroll into Intune. If the windows devices are all enrolled into Intune, we can use device.deviceOSType -eq "Windows" and device.managementType -eq "MDM" for the dynamic group rule.
Hope it can help.
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