Outpatient Surgery Quality and Access Act of 2021 This bill establishes and modifies certain requirements relating to Medicare payments for ambulatory surgical center (ASC) services. Specifically, the bill (1) requires the payment system for ASC services to feature certain positive annual adjustments equivalent to those made with respect to hospital outpatient department (OPD) services; (2) revises quality reporting requirements to permit publicly available, side-by-side comparisons of quality measures for ASCs and OPDs in the same geographic area; and (3) requires the Centers for Medicare & Medicaid Services (CMS), when excluding requested procedures from the list of those approved to be performed in ASCs, to cite specified reasons for doing so. With respect to excluding procedures from the approved list for ASCs, the CMS may not cite as a basis for exclusion that a procedure can only be reported using an unlisted surgical procedure code. (Physicians sometimes use unlisted codes when performing new procedures or services if no existing code is adequately descriptive.) The bill also limits the copayment amount for ASC services under Medicare to that of the inpatient hospital deductible.