Birthright Citizenship Act of 2021 This bill limits birthright citizenship by redefining what it means to be subject to the jurisdiction of the United States. Currently, a person born in the United States and subject to U.S. jurisdiction is entitled to citizenship. Under the bill, a person is subject to U.S. jurisdiction if he or she is born to a parent who is (1) a U.S. citizen or national, (2) a lawful permanent resident residing in the United States, or (3) an alien performing active service in the Armed Forces. The bill does not affect the citizenship or nationality status of any person born before the bill's enactment date.