Black Lung Benefits Improvement Act of 2021 This bill revises requirements for miners' claims for pneumoconiosis (black lung disease) benefits. Specifically, the bill requires the Department of Labor to pay the attorneys' fees of specified parties on a qualifying benefit claim, give a claimant the opportunity to substantiate a claim for benefits through a pulmonary evaluation, authorize a CT (computerized tomography) scan in diagnosing complicated pneumoconiosis, educate certain individuals who work on black lung benefits about medical evidence relevant to claims, establish criteria that a mining operator must meet to self-insure against claims, and develop a strategy to reduce delays in adjudication of black lung disease benefits claims. The bill also requires the Government Accountability Office to report on barriers to health care faced by coal miners with black lung disease. The bill authorizes (1) black lung disease clinics to use federal funds to help individuals file claims, and (2) certain previously denied claimants to file a new claim for black lung disease benefits within one year. The bill prohibits a person from (1) knowingly and willfully making a false statement or misrepresentation in increasing or reducing black lung disease benefits, or (2) threatening or misleading a participant in a proceeding regarding such benefits. Further, the bill revises (1) the standards of medical evidence that establish a presumption that a miner is totally disabled by black lung disease, and (2) payments to such miners. Lastly, the bill provides statutory authority for the Office of Workers' Compensation Programs.