Hi, I have a NUC8i7beh. with a Dell TB16 Thunderbolt dock and dual monitors on the Displayport and HDMI ports.
If both monitors are plugged into the TB16, only the displayport works. To get both monitors working, I have to use the HDMI on the back of the NUC, so when I plug my laptop into the expansion box, I have to take the HDMI out of the NUC.
Everything else works through the expansion box - keyboard, mouse, external storage.