I’ve seen similar issues happen with USB-C ports before. Sometimes it’s related to drivers or BIOS updates rather than the hardware itself. It might be worth checking for the latest drivers or running Dell diagnostics to see if the port is detected properly.

@Dell-Jordan 
Some Precision Systems with USB Type-C Port Lack a Thunderbolt 3 Controller
kbdoc  000130984

You may encounter an issue where a Dell Latitude system with a USB Type-C port will not support a connection to a Thunderbolt 3 device (such as a Dell Thunderbolt Dock (TB16). This is a result of either:
The system does not meet the hardware requirements for Thunderbolt 3
The system has the capability but was not ordered with an OPTIONAL Thunderbolt 3 controller

Cause
NOTE: If the system was not ordered with the Thunderbolt 3 options, it cannot be added at a later time.