We had a requirement to hide users tab from task manager for WVD session hosts, I tried to find a suitable GPO for that but there is nothing as such.. So I have found this GPO to hide other users apps in task manager which seems to be useful.
Computer Configuration/Administrative Templates/System/Logon/Hide Entry Points for Fast User SwitchingChange the above to Enabled
Users can see the other users applications in the task manager
If you see the below, In the first task manager techgeniususer1 can see only his application and the drop down for user 2 is disabled.
Like wise in the second task manager techgeniususer2 can see only her application and the drop down for User 1 is disabled
To download Administrative Templates (.admx) for Windows 10 May 2020 Update (2004) https://www.microsoft.com/en-us/download/101445