National Police Misuse of Force Investigation Board Act of 2021 This bill establishes the National Police Misuse of Force Investigation Board as an independent federal entity. Among other duties, the board must investigate deaths that occur in police custody, officer-involved shootings, and uses of force that result in severe bodily injury in police custody. The board must also report periodically to Congress, federal entities, and state and local governments on recommendations to reduce incidents of misuse of force by law enforcement. The bill requires a state or local government that receives funding under the Edward Byrne Memorial Justice Assistance Grant program to (1) allow findings and recommendations of the board to be admissible in court, and (2) report on actions taken to address the recommendations of the board. The Department of Justice may reduce allocations to states and local governments that fail to comply with these requirements.