I have two USB-C Ethernet adaptors:
I've used the AmazonBasics one for a while and I've no idea when it stopped working. I automatically get connected to the Wi-Fi, so I'm unsure when the adaptor become useless.
It may well have been after I upgraded to macOS 11 Big Sur. I purchased the second one, assuming the broken adapter, this week.
I have two laptops, with exactly the same behaviour:
MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports)
MacBook Pro (15-inch, 2017)
The Ethernet cable does work; I am able to use it, without the adaptors, on my PC successfully.
However, on my Mac machines, "Network Properties" doesn't show that it's connected. I removed the additional network interfaces, hoping that it would readd them when it was the device again, but no such luck. Creating a new Thunderbolt Bridge simply shows as "Not Connected".
I've read in other question:
that a possible (although frowned upon) solution would be to disable the authentic certificate check Apple does to secure hardware. However, in my System Information, none of the four Thunderbolt connectors are connected to anything.
"USB" lists only the internal devices, like the keyboard and web cam.
Any ideas what could be wrong?