PACE Part D Choice Act of 2021 This bill allows Medicare-only beneficiaries who are enrolled in Programs of All-Inclusive Care for the Elderly (PACE) to choose prescription drug plans that are not operated by PACE. (PACE is a program under Medicare and Medicaid that provides in-home and community services for certain individuals as an alternative to nursing home care.) Specifically, the bill allows PACE enrollees who are Medicare (but not Medicaid) beneficiaries to choose a prescription drug plan that is not a Medicare Advantage plan or operated by PACE and for which annual out-of-pocket costs and federal subsidies are equal to or less than that under the applicable PACE prescription drug plan. The bill also allows for disenrollment from a chosen plan upon a change in medication or demonstration of an unexpected increase in out-of-pocket costs. PACE programs must conduct outreach, monitor data, and coordinate benefits with respect to such options.