Surface Laptop not displaying through USB-C connected Monitor

From Troubleshoot problems with USB-C on Surface - Microsoft Support

 

Unplug your USB-C device, then shut down your Surface by selecting Start  > Power > Shut down. After 10 seconds, press and hold the Power button for about 20 seconds until the Windows logo appears, disappears, then appears again. After that, plug in your USB-C device again.