How can an Administrator Discreetly View a Remote Desktop User's Session?

Set the Remote Control settings to view the session with the "Require user's permission" checkbox unchecked. You can set this setting on both the user account and the RDP protocol on the server but the server setting over-rides the user account setting. Also make sure this isn't being set to a conflicting setting via GPO. When the manager "connects" to the user's session the user will see a very brief blip of the screen but otherwise won't know that someone is shadowing their session.

Just found an answer for this and tested it. I Hope it will help someone else. Here is part taken from the Source.

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2. Type quser.exe to determine the session number of the user session you want to shadow.

3. In this example, the Administrator is going to shadow the user1 session which is session 3. You need to know the session number (“3”) for the next step.

4. Start shadow session by typing mstsc /shadow:# /control where # is the session number to shadow and /control allows you to control the session.

Source: https://www.riptidehosting.com/blog/how-to-shadow-a-users-remote-desktop-session-on-windows-2016-in-workgroup-mode/