iMac 2020 27" ethernet will not connect

The trouble I find with Apple's Diagnostics, is if it can't find a piece of HW it'll just skip that test.

In System Settings>Network, try adding an ethernet port.

In System Report>Hardware, does anything show under Ethernet Cards, or System Report>Network?

To find out if it's system wide or user specific, try this...

Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.

Does it work in the new account?

Gulp, Ethernet & Lightening don't get along well, I suspect it's dead. :(

No idea what number is missing from 202, but look for...

https://www.amazon.com/usb-ethernet-adapter/s?k=usb+ethernet+adapter

https://www.amazon.com/ethernet-Adapter-Supporting-Ethernet-Network/dp/B084MCVVP9?th=1

They have them in USB-C also.

Remove the dock and go directly to the Mac with a new Ethernet cable and try and reestablish a connection.

Your dock may be fried as well all the cables. Surprisingly enough, over voltage effects even mundane parts such as cables.

I have no idea if it's Passé now days, but every sensitive electronic device should be on a surge protector. Shutting down a wall powered device does not necessarily eliminate the electrical pathway. If there is a "hard break" in the path the amount of electricity a lightening strike delivers can easily jump tiny switches inside a Mac. With a surge protector, and even then, the only protection from lightening, without a whole house arrestor system, is to physically unplug the device from the house electrical system.