Is it easy for American postdocs to get a green card?

If you can't take the exam directly, you need to apply, and it is not good for a simple postdoctoral student to apply. You need to have some local work experience.

The American permanent resident card, also known as the green card, is an identity document used to prove that foreigners have the status of permanent residents in the United States.

The legal permanent residency of green card holders is an official immigration benefit, including conditional permission to stay in the United States and get a job. The holder must maintain his permanent resident status, and if he no longer meets certain conditions required by the status, the holder may lose his status.