Is there a difference between having an American green card and becoming an American citizen?

The green card is the proof that the United States grants immigrants permanent residency in the United States. Green card holders call them permanent residents, but they are not equal to American citizens. American citizenship means American citizenship.

Naturalization to the United States: Holding an American passport is an American citizen, and it is an American nationality. It enjoys all the rights of American citizens, including the right to vote and stand for election, and can retain American citizenship even if it does not live in the United States for life.

American green card: the so-called "American green card" only has "permanent residency in the United States" and is not an American citizen. It has no right to vote and stand for election. You must live in the United States for a period of time every year (18 1 day) to keep this green card. If you don't live in America for many years, you will lose this green card. Many China people have American green cards, but they still have China passports and China nationality.