Struggling to get USB-C DP to work

[Arwen]

There are several things related to external displays on a Pinebook Pro;

• Must be USB C alternate mode Display Port
  
• If the laptop dock is USB C alternate mode HDMI, it will never work
  
• Some laptop docks use USB Display Link, which is basically a USB attached video card. These require drivers on the Pinebook Pro and maybe slower.
  

Checking your device it "appears to be using USB C alternate mode Display Port". Notice to quotes. It appears to be. That's part of the problem, manufactures not being crystal clear in their specifications.

So, try several other OSes and see if they work with your laptop dock. If so, then it's a software problem. Not "USB C alternate mode HDMI", which will never work with the Pinebook Pro.