I have found USB-C docking stations a minefield - found your post, re-watched Jay’s docking station video you mentioned (realised I had already seen it and forgotten the advice) and now sorted my issues with my Lenovo L480 laptop and 2x HDMI displays.
I first inadvertently bought a Lenovo USB-C 40AF0135UK dock for £85 on eBay, which did not work at all even though I installed the proprietary Displaylink package onto PoPOS 21.04. Very disappointed I had not listened to Jay. I tested it with Windows 10 and it worked fine streaming 4K to two displays - so will confidently resell on eBay stating clearly it is only suitable for Windows.
Second attempt (remembering Jay’s advice - stick to standards) was a Lenovo Thunderbolt 3 40AC dock on eBay for £73. Had issues (coming to that in a sec) and thought I had bought another failed dock for Linux. I did not realise the USB-C port on my Lenovo L480 laptop that is labelled for charging is NOT a Thunderbolt port. The documention for the L480 don’t make it at all clear. There is a second port that does not even look like USB-C located closer to the front of the laptop, which is intended for the physical dock connection, which takes the Thunderbolt 3 connector fine, and BOOM the display ports on the dock came to life.
Thunderbolt provides (by design) DisplayPort, which is supported by the hardware. No drivers. As Jay said in his docks video - stick to standards to avoid problems.
Thanks to Jay for the good advice, I should have listened. Thanks to the poster of a forum (I cannot remember which) about the L480 Thunderbolt port being separate to and located in front of the USB-C charging port.
I have found that PopOS/Ubuntu is not happy about me disconnecting displays and reconnecting them. It doesn’t always come back and I get a blank display, so I have to reboot. Odd.