Department of Homeland Security Appropriations Act, 2021 This bill provides FY2021 appropriations for the Department of Homeland Security. The bill provides appropriations for Departmental Management, Operations, Intelligence, and Oversight, including the Office of the Secretary and Executive Management; the Management Directorate; Intelligence, Analysis, and Operations Coordination; and the Office of the Inspector General. The bill provides appropriations for Security, Enforcement, and Investigations, including U.S. Customs and Border Protection, U.S. Immigration and Customs Enforcement, the Transportation Security Administration, the U.S. Coast Guard, and the U.S. Secret Service. The bill provides appropriations for Protection, Preparedness, Response, and Recovery, including the Cybersecurity and Infrastructure Security Agency, and the Federal Emergency Management Agency (FEMA). The bill provides appropriations for Research, Development, Training, and Services, including U.S. Citizenship and Immigration Services, the Federal Law Enforcement Training Centers, the Science and Technology Directorate, and the Countering Weapons of Mass Destruction Office. The bill also sets forth requirements and restrictions for using funds provided by this and other appropriations Acts.