United States Commission on an Open Society with Security Act of 2021 This bill establishes the United States Commission on an Open Society with Security to study how the government may provide for both security in, and public access to, federal buildings and other federal property and sites. The commission shall examine (1) government and private security practices and proposals, building design, public space management, counterterrorism needs, and refurbishment of existing federal facilities; (2) the effect of access to public facilities and spaces on constitutional rights and civil liberties, economies of affected jurisdictions, architectural aesthetics, traffic and congestion, and employee job performance; (3) technology to augment or replace traditional modes of security; and (4) methods of assessing the risks posed by terrorism, balanced against the needs and values of open access.