To use the Microsoft Lumia 950 with an external display like the LG Thunderbolt Monitor 34UM95, you will need to use the Microsoft Display Dock.
To begin with, we will need the following devices:
C. USB-C to USB-C cable
D. DisplayPort to DisplayPort cable
E. USB-C power adapter (which comes with Microsoft Display Dock)
F. LG Thunderbolt Monitor 34UM95
First of all, the Microsoft display dock needs to be powered by a USB-C power adapter as shown in Figure a.
Figure a.
Step 1: Connect power to the dock as shown below in Figure a. If the dock is powered, the light above the USB-C connector in Figure b will light up in red.
Figure b
Step 2: Connect the Display Dock to the Lumia 950 with the USB-C to USB-C cable.
Step 3: Connect the Display Dock to the LG Thunderbolt Monitor with the DisplayPort to DisplayPort cable.
Step 4: Adjust the display source on the LG Thunderbolt Monitor to DisplayPort. Once you're connected, the light in Figure b will turn white. At the same time, the Lumia 950's screen will go into Continuum Touchpad mode as per Figure c which turns the phone into a touchpad for the display.
Figure c
Once your connection is successful, you should see the Windows desktop on the LG Thunderbolt Monitor as per Figure d.
Figure d
The LG Thunderbolt Monitor 34UM95 works great with the Microsoft Display Dock connected over DisplayPort.