U2719DC, two on CalDigit dock not at full resolution

cleef,

 Since both U2719DC worked flawlessly on the third ThinkPad X1 Extreme Gen 2, GeForce GTX 1650 laptop, this proves that they are working. As to why the other two ThinkPads have issues, unknown. You should post on their forums =
https://dell.to/3eTv54A

@cleef  In order to run dual QHD through a dock that also wants to run USB 3.x data, which pretty much every dock will, you need one of the following:

• A system and dock that both support DisplayPort 1.4/HBR3 over USB-C rather than DisplayPort 1.2/HBR2 over USB-C.
• A system and dock that support Thunderbolt 3.  (In this case, you can run dual displays up to 4K 60 Hz each even from a DP 1.2/HBR2 system.)

DP 1.4/HBR3 support is still fairly rare on systems today, and I don't think the CalDigit dock you're referring to supports it.  It DOES support Thunderbolt 3, as does the X1 Extreme you're using.  But the T14 and T490s both support Thunderbolt 3 as well, to my knowledge, so if they're not working properly, there are some possibilities here:

• Thunderbolt might have been disabled in the BIOS
• Thunderbolt software might not be installed within Windows.
• You might not have "approved" the dock as a Thunderbolt device within Windows.

In any of the situations above, the CalDigit dock would fall back to USB-C backward compatibility mode, which means it will only be able to tap into 25% of the video bandwidth it would be able to if it was using Thunderbolt 3.  So check your BIOS settings, verify Thunderbolt software is installed, then check Thunderbolt Control Center to verify that the dock is detected and approved.  If all that fails, update your BIOS, drivers, etc.

As for the GPU in use, the T14 probably has the MX330 using NVIDIA Optimus, which basically means the Intel GPU controls all display outputs, while the NVIDIA GPU acts as a render-only advice that activates only when needed and passes completed video frames to the Intel GPU for output to displays.  Optimus is the more common setup on laptops that have dual GPUs because of the battery life benefits of being able to power down the discrete GPU completely when no graphics-intensive activity is going on.  By comparison, the X1 Extreme has the NVIDIA GPU wired directly to the display outputs.  This has some battery life consequences, but it also makes it possible to use certain technologies that aren't possible through Optimus, including VR, G-Sync, and possibly higher resolutions and DisplayPort revisions, depending on how the specific Intel and NVIDIA GPUs installed in the system.  (In the case of the GPU combination found in the X1 Extreme Gen 2, having the NVIDIA GPU directly controlling the disply outputs allows the system to support DisplayPort 1.4/HBR3, which allows 4K 60 Hz HDR and also 5K (5120x2880) displays, neither of which would be possible if the Intel GPU in that system controlled the outputs.  The NVIDIA GPU can also run up to 4 displays, whereas the Intel GPU is limited to 3, but if you keep the Intel GPU running the built-in display as is the default on that system, this setup means you can run up to 5 simultaneous displays as long as their resolutions, refresh rates, and cabling fall within some complex restrictions.  I've done that myself on my own X1 Extreme Gen 2.)

Thank you very much! That solved it for me. I had to use the other, not so obvious USB-C port which indeed supports Thunderbolt 3.

Everything works now.