Right-click the target connection and choose "Disconnect" from the context menu. Click "OK" to kill the session.
How to Kill Remote Desktop Sessions
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You may create an event monitor for this. When there is a disconnected user session, there will an alert. Then you can create an alert view for this specific monitor, with the view, you should be able to see all server with disconnected user session.
Find disconnected RDP sessions - TechNet Microsoft
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Remote Logoff in PowerShell In the example above, 'abertram' is logged into the remote computer in session 2. Using the logoff command, we simply need to pass the session ID to the command as an argument and it will dutifully log the user off as expected.
How To Log Off Windows Users Remotely With PowerShell
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