National Infrastructure Bank Act of 2021 This bill creates the National Infrastructure Bank to facilitate the long-term financing of infrastructure projects. Specifically, the bank must provide loans to public and private entities for financing, developing, or operating eligible infrastructure projects. An eligible project must have a public sponsor as well as local, regional, or national significance. The bill treats the bank as a government corporation exempt from tax and treats contributions to the bank as charitable contributions. The bill also provides for criteria and preferences for deciding whether to provide a loan, such as whether a project promotes job creation or provides environmental benefits. Projects that receive a loan must (1) pay all laborers and mechanics locally prevailing wages, and (2) use only certain U.S.-produced construction materials unless a waiver is secured from the bank. The bank shall issue stock and may also issue bonds and maintain a discount line of credit with the Federal Reserve System. The bank must apply for a national bank charter and, once chartered, accept deposits from individuals, corporations, and public entities and pay interest on those deposits. The bill imposes requirements related to the bank's operation, such as minimum reserve requirements and requirements for handling loan losses. In addition, the bank must facilitate the organization of at least seven regional economic accelerator planning groups to, among other activities, identify infrastructure needs and priorities. Within five years, the Government Accountability Office must report on the bank's activities.