Ironically, my predecessor setup (which was a Dell latitude with an E-port replicator) just received driver / firmware updates about 3 weeks ago. It is now comfortably able to run the two monitors both at 4K resolution simultaneously even though it does not have any Thunderbolt or USB-C interface at all. This is a real disappointment because having two 4K monitors was the most compelling reason for me to spend the money on upgrading my system in the first place. Unfortunately, after setting the first (primary) monitor to 3840 x 2160 the highest resolution setting offered for the second monitor is only 1920 x 1080.
Nonetheless, pior to my purchase of the whole setup I was led to believe that it would still be adequate to run my two 4K monitors (connected by Display port through my TB-3 Dock which is the 40AC model).
My ThinkPad X1 Tablet 3rd Generation has an Intel UHD 620 Graphics Card -which I realise has no standalone GPU.
