Restoring Resilient Reefs Act of 2021 This bill addresses the conservation and sustainability of coral reef ecosystems. Among other things, the bill reauthorizes through FY2026 and revises various activities under the Coral Reef Conservation Program; requires the National Oceanic and Atmospheric Administration (NOAA) to establish standards for identifying individual coral reefs and ecologically significant units of coral reefs; directs NOAA to provide block grants to states to support state coral reef management and restoration; directs NOAA to designate two reef research coordination institutes to advance and sustain essential capabilities in coral reef research; provides statutory authority for the U.S. Coral Reef Task Force to lead, coordinate, and strengthen federal government actions to preserve, conserve, and restore coral reef ecosystems; authorizes the Department of the Interior to provide scientific expertise, technical assistance, and financial assistance for the conservation and restoration of coral reefs; and establishes a National Coral Reef Management Fellowship Program.