Fantastic, thank you for taking the time to report back.

I would like to say I have had odd issues with USB-C on my Lenovo T480. I cant say exactly what had happened that started this, but as per the original poster I installed all the latest drivers from Lenovo, which included a Thunderbolt firmware update and this so far has cured the issue (DisplayLink/Dell D6000 not appearing in Display Adaptors)

PS - I have attempted to run the Dell Firmware Update utility and had no luck. Its a very poorly written app (extracted the files with 7zip to)

Band-aid fix found to make functional.
 

I found a work around as I had the same issue on a brand new HP elitebook 830 g8 where displays and everything was functional on USB 3.0 but display would not show up in USB-C (but peripherals and charge would work). To fix all I had to do was disable the thunderbolt controller in device manager, then hook up through USB-C where it then recognized the dock.
https://i.imgur.com/xigQdxx.png
Unfortunately I need to leave Thunderbolt disabled to connect to the dock and can then re-enable but if it is enabled before connection it stops working like before. Hoping I can uninstall and reinstall the Thunderbolt controller software but so far not having much luck making it work without constant disabling.