Bank Merger Review Modernization Act of 2021 This bill establishes additional requirements for bank mergers and acquisitions, including by requiring approval from the Consumer Financial Protection Bureau for certain mergers involving a provider of consumer financial products, financial regulators to determine that the public benefits of any merger outweigh the costs, specified community reinvestment ratings, and institutions to meet certain financial stability standards and stress testing. Further, financial regulators must assess the competitive effects a merger will have on the market for certain financial products. Additionally, applicants for a bank merger must disclose specified communications regarding the proposed merger. The bill also provides citizens with standing to file a civil action to review a merger approval.