If you own a ThinkPad P1 or X1 Extreme and connect it to an external monitor on Windows 10, then the chances are that you have experienced sluggish performance with your device set to "Second screen only". Lenovo finally released an update to address the issue, but then pulled it without reason. Fortunately, we still have the download link to the package if you need it.
https://www.notebookcheck.net/Lenovo-resolves-ThinkPad-P1-and-X1-Extreme-s-second-screen-low-framerate-bug-then-pulls-the-update-that-fixes-it.447060.0.html