Preventing Radical Extremist's Violent Endeavors Now and Tomorrow Act of 2021 or the PREVENT Act of 2021 This bill expands the duties of the Office for State and Local Government Coordination in the Department of Homeland Security to include, for purposes of countering violent extremist threats (1) providing training from specially trained clinical social workers, psychologists, religious and community leaders, and law enforcement personnel to assist local efforts in securing the homeland; and (2) in coordination with the Federal Bureau of Investigation, providing to state and local governments specialists, analysts, and agents trained to counter terrorism and white nationalism to assist local efforts at responding to such threats.