After reading the post from @Daniel_Power, I am revisiting how I was testing my Startech dock https://www.startech.com/en-us/cards-adapters/tb3dk2dppd.
The manual is listed here.
In reading this thread about which ALT mode is supported
the docking station will be limited based on the docking station chipset and/or cables .
In my initial testing I am getting the same result as everyone - the docking station has 1 monitor working via display port, but the second monitor does not work from the station. If I plug that monitor’s cable directly to the laptop, then the monitor works.
Upon looking at the technical document (via the pdf):
DP alt mode (DisplayPort alternative mode)
This docking station supports DP alt mode, which means a DisplayPort video signal
can be transferred over a USB-C cable. Thunderbolt 3 supports the full USB-C standard,
including support for DP alt mode. Because the docking station supports DP alt mode,
you can connect Thunderbolt 3 or USB-C based video devices, cables, or adapters to
the secondary Thunderbolt 3 port on the rear of the docking station.
While the manual references to this dongle ( CDP2HD4K60 ), I was not able to find this exact module via Amazon; Amazon recommended me this model CDP2HD4K60H. During the initial testing, the dongle connected with a HDMI cable works better than any previously USB-C to HDMI cable.
When I plugged the dongle/HDMI into dock’s USB-C port, the two external monitors are working. In fact, the laptop monitor is working. With the three displays, I noticed the laptop screen was not responding. I can disconnect the USB-C cable, but the laptop’s monitor was frozen.
As I am using POP!_OS 21.10, I have not tried using Windows (or using drivers specific to the chipset).
I am lead to think the laptop might work as long as the requirements/circumstances are met correctly.
Hope this helps,