Where is the conection for Ethernet cable on new 24" iMac?

There is no physical port on the 2021 iMac. As your screenshots show, it's on the power brick.

You would plug the other end of the ethernet cable into either an ethernet switch or into your cable modem. The power brick handles all the IO between the internet and your iMac. You simply just need to feed the brick the Internet.

Only if you buy the four-port 8/8-core model, or special order that power supply on an entry-level two-port model, a US$30 option.

I believe the OP was demonstrating where it is, not asking. That's how I read it.