Stars and Stripes Act of 2021 This bill prohibits the Department of State from displaying any flag or banner at a diplomatic or consular post other than specified flags. Such flags are (1) the U.S. flag; (2) the flag of the country wherein the post is located; (3) the flag of a state, territory, or possession of the United States; (4) a departmental or secretarial flag; (5) the flag of an Armed Force; or (6) a flag to honor prisoners of war or those missing in action.