On my previous Macbook Pro 16in Intel (Monterrey) and before, have always had my computer connected to OWC thunderbolt dock, and thunderbolt usb-c 10g ethernet attached to the dock getting me about 1.7gbps.
On the new M1 MacBook Pro 14 (Monterrey - Stable version shipped with), it still works but now in Preferences > Network > Thunderbolt Bridge shows as not connected (even though it is). The problem here, is even though I have that set to override wifi, wifi appears first in the list and thus uses the wifi because it thinks the ethernet isn't connected. If I disable wifi, then thunderbolt bridge is on top, still says not connected, but able to get full ethernet speeds. But then when I unplug and want to use wifi i have to manually re-enable wifi.
Not sure why system preferences thinks the Thunderbolt Bridge (10g ethernet isn't connected when it is on my new M1?) Is this solved in the 12.1 beta, if so will update to that.