Hi Steve,
Is it possible to publish the built-in applications of windows system (such as Paint, Notepad, Calculator etc.) to see if they can work?
If only Office can’t work, please refer to the following link:
https://learn.microsoft.com/en-us/deployoffice/deploy-microsoft-365-apps-remote-desktop-services
There are special requirements for deploying MS Office as a RemoteApp.
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Best Regards