Windows’s built-in RDP client has a checkbox for using all your monitors to display the remote session, but no control allowing you to select only a subset of your monitors. There is a way around it, though. Thanks to Scott Hanselman for the information.
To do this, save the connection info as an RDP file. Open the RDP file in a text editor, and set the parameter usemultimon to 1 (usemultimon:i:1). Then, run the command mstsc /l to list the ID numbers of your screens. Find the numbers of the monitors you want to use, and set them on the selectedmonitors parameter. E.g, selectedmonitors:s:1,2.
usemultimon:i:1
selectedmonitors:s:1,2If the parameters don’t already exist in the RDP file, add them. Finally, save the RDP file, and double-click it to launch the connection.