@maxgoedjen Yes, you’re correct, 27MD5KL-B is the newer model that supports iPad Pro via USB-C, and 27MD5KA-A is the older model that is Thunderbolt 3 only.
Since the support document for the newer display model says that it requires a Mac with a USB-C port or Thunderbolt 3, I remain hopeful that the DTK is compatible, but I have not received official confirmation that this is so:
The new LG UltraFine 5K Display (Model 27MD5KL-B) requires a Mac with a USB-C port or Thunderbolt 3 (USB-C) port running macOS Mojave 10.14.6 or later, or an iPad Pro with a USB-C port running iOS 12.4 or later. https://support.apple.com/en-us/HT210205