Resetting the Impact Act of 2021 or the TRIA Act of 2021 This bill requires certain data collection and recommendations relating to a Medicare post-acute care prospective payment system to incorporate the effects of COVID-19 on providers and patients. Current law requires the Centers for Medicare & Medicaid Services (CMS) and the Medicare Payment Advisory Commission to develop a prototype for a unified Medicare payment system for post-acute care that is based primarily on patient characteristics (e.g., cognitive ability, functional status, or impairments) rather than the provider setting (e.g., skilled nursing facility, home health agency, inpatient rehabilitation facility, or long-term care hospital). The bill requires the prototype to account for the role of post-acute care providers during public health emergencies, particularly in light of the COVID-19 emergency and the related effects on such providers and their patients. The bill also delays the development of the prototype until two years after the later of January 1, 2022, and the date by which the CMS has collected eight calendar quarters of data after the emergency ends and other changes have been implemented.