Thank you for posting here.
From the following link, we can see if we want to use "WMI Filter" to filter "Windows Server Roles", it is
"root\CIMv2" instead of "root\CIMv2\TerminalServices".
So if you want to filter Desktop OS and terminal servers to apply GPO, you can try:
SELECT * FROM Win32_OperatingSystem WHERE ProductType="1"
SELECT TerminalServerMode FROM Win32_TerminalServiceSetting WHERE TerminalServerMode = 1
Hope the information above is helpful.
If the Answer is helpful, please click "Accept Answer" and upvote it.
I have now created a separate GPO with the same settings as my original, applied the terminalserver WMI filter to it, and enabled loopback processing to capture user settings specifically for that machine.
The GPO side of things is working, now I have another issue with remote desktop services I am looking into that prevents the GPO settings from applying.