Do you have administrator permission to make changes on your remote TS?
If yes, you can set below group policy on the remote terminal server.
Computer Configuration\Administrative Templates\Windows Components\Remote Desktop Services\Remote Desktop Session Host\Remote Session Environment - Limit number of monitors Enable it and set the value as 1
If you do not have the permission, we suggest that you could use mstsc to remote connect to the TS.
Show Options > Display > uncheck Use all my monitors for the remote session
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