Thunderbolt Bridge Not Connected in Big Sur

Hi everybody.

My Thunderbolt Bridge Connection used to work just fine. But then I noticed, that it suddenly had disappeared from the Network Preferences Pane. Did not notice before, because my WiFi still was an excellent backup and took over without my awareness.

Some other answer in this forum (link) that did not work for me but got me to this idea that straightened things out:

1. Open Preferences
2. Select Network
3. Select your not connected Thunderbolt Bridge (or add one via the plus at the bottom of this pane)
4. Open the "Manage Virtual Interfaces..." Menu-Item within the Options-Symbol (Three dots in a circle)
5. Click on the Pencil-Icon which takes you to the "interfaces to include..."
6. Deselect the now ticked false Interface, which is just a Service not hooked up to anything
7. Select the correct Hardware-Interface from the list, either your Display or in my case the Thunderbolt Ethernet Adapter
8. Click Done. Click Done. Click Apply.
9. Open the "Set Service Order..." Menu-Item within the Options-Symbol (Three dots in a circle)
10. Drag the Thunderbolt Bridge to the top of the list if this is the speediest connection you have
11. Click OK. Click Apply.

Not sure if there is a Restart required after this.

This did the Trick for me.

Good luck.