Postal Service Reform Act of 2021 This bill addresses the finances and operations of the U.S. Postal Service (USPS). The bill requires the Office of Personnel Management to establish, within the Federal Employees Health Benefits Program, the Postal Service Health Benefits Program for USPS employees and retirees and provides for coordinated enrollment of retirees under this program and Medicare. The bill repeals the requirement that the USPS annually prepay future retirement health benefits. Additionally, the USPS may establish a program to enter into agreements with an agency of any state government, local government, or tribal government, and with other government agencies, to provide certain nonpostal products and services that reasonably contribute to the costs of the USPS and meet other specified criteria. The USPS must develop and maintain a publicly available dashboard to track service performance and must report regularly on its operations and financial condition. The bill requires mail delivery to occur at least six days a week. The Postal Regulatory Commission must annually submit to the USPS a budget of its expenses. It must also conduct a study to identify the causes and effects of postal inefficiencies relating to flats (e.g., large envelopes). The USPS Office of Inspector General shall perform oversight of the Postal Regulatory Commission.