Can you detach the primary interface (eth0) on my EC2 instance?
No. You can attach and detach secondary interfaces (eth1-ethn) on an EC2 instance, but you can’t detach the eth0 interface.

https://www.interviewquestionspdf.com/2017/01/can-you-detach-primary-interface-eth0.html
No. You can attach and detach secondary interfaces (eth1-ethn) on an EC2 instance, but you can’t detach the eth0 interface.