Iron Dome Reinforcement Act of 2021 This bill prohibits certain foreign assistance to the Palestinian Authority or the Palestine Liberation Organization (PLO) unless the Department of State certifies to Congress that the receiving entity (and its officials and agencies) has ceased paying compensation or benefits, other than benefits that are generally available to Palestinians, to the families of Palestinians killed in connection with committing an act of terrorism. The State Department shall periodically report to Congress on whether such requirements are being met. If they are not, foreign assistance that would have gone to the Palestinian Authority or the PLO shall be made available as assistance to Israel for its Iron Dome anti-rocket defense system.