I had this same issue with an LG OLED monitor. I'm not 100% sure this was the solution as it was long ago, but you need to NOT have the USB-C power cable connected to the dock, just the HDMI. Connect the Deck to the dock and you'll get image. After this you can plug the dock back to the power cable.
I had this same issue with an LG OLED monitor. I'm not 100% sure this was the solution as it was long ago, but you need to NOT have the USB-C power cable connected to the dock, just the HDMI. Connect the Deck to the dock and you'll get image. After this you can plug the dock back to the power cable.