Harnessing Opportunities by Pursuing Expungement Act of 2021 or the HOPE Act of 2021 This bill authorizes the Department of Justice (DOJ) to make grants to states and local governments to reduce the financial and administrative burden of expunging convictions for state cannabis offenses. The bill also requires DOJ to study and report on (1) the effects on an individual of a criminal record report of a conviction for a criminal offense related to cannabis, and (2) the costs incurred for incarcerating an individual for a criminal offense related to cannabis.