MacBook – Ethernet via Thunderbolt display with MacBook Pro 2017 (A1707)

This question may be a duplicate. Try some of the suggestions here: How to force Thunderbolt-ethernet connection when switching networks without restarting computer?

It sounds to me like an issue with connecting to your router.

Try the suggestion to renew your DHCP lease under System Preferences > Network Preferences > Advanced for the Thunderbolt Ethernet. Or if you have a static IP address, make sure the right IP address, Subnet Mask, and the correct DNS server are entered.

Is there a reason you are trying to go through the Thunderbolt Bridge setting and not Thunderbolt Ethernet?

Also click on the Apple icon in the Menu Bar and look at your Locations. If something other than Automatic is selected, those Location preferences could be stopping your MBP from connecting to the Router. You will also see this at the top of the Network Preferences for your connection.

UPDATE

Is there a reason you are trying to go through the Thunderbolt Bridge setting and not Thunderbolt Ethernet?

I asked you this above. When I looked at my MBP connected with a Thunderbolt Ethernet Adapter, I checked under Thunderbolt Bridge and saw the exact message you have.

The thing is that I am Connected via Thunderbolt Ethernet and all of my configurations for my connection to the router are there.

The Thunderbolt ports can be used as regular miniDisplayPorts. Modern Dell screens have DisplayPort or miniDisplayPorts. The only difference to HDMI is that DP supports higher resolutions.