Strengthening Digital Identity Act of 2021 This bill directs the National Institute of Standards and Technology (NIST) to take into account strengthening identity proofing under the program to support the development of voluntary and cost-effective technical standards, metrology, test beds, and conformance criteria for identity management. NIST shall develop and implement a technical roadmap for identity management research and the development of standards and guidelines focused on enabling the use and adoption of modern digital identity solutions. NIST shall develop and periodically update a framework of standards, methodologies, procedures, and processes as a guide for federal, state, and local governments to follow when providing services related to digital identity verification.