What is the difference between "American citizens who immigrate to the United States" and "Native American citizens"?

There is not much difference. They are all human beings. But from the political and physiological aspects, there are the following differences:

First, basically all immigrants are not of the same color, and English pronunciation will have their local accent.

Second, immigrants are basically discriminated against by local Americans, unless you are very good and powerful, making them speechless.

Third, there are three kinds of "Native American citizens": Indians, the first settlers (whites) a hundred years ago, and African slaves (blacks) brought by the first settlers at that time.

Are you clear now?