Hi Derek Crossley1,
Thank you for reaching Microsoft Community.
Just to make sure first: you would like to make your Surface Pro 9 as the second screen of your other laptop through USB-C connection, correct?
If yes, I'm sorry but this is not possible. To make the Surface a second screen for another laptop, it can only be done through wireless projection with the Project to this PC feature. See this page for details: Screen mirroring and projecting to your PC - Microsoft Support
Kind regards,
Marrion