Protecting Benefits for Disabled Veterans Act of 2021 This bill provides statutory authority for the Department of Veterans Affairs (VA) to assign, for purposes of the disability compensation program, a disability rating of total to a veteran who meets certain parameters and is unable to secure or maintain substantially gainful employment due to a service-connected disability. Specifically, the VA may make such a disability determination if a veteran has a service-connected disability rated at least 60%, or has two or more service-connected disabilities with one being at least 40% and a combined total of at least 70%. The VA may also make a determination on the disability rating in circumstances where a veteran meeting the specified parameters maintains marginal employment (income is less than the poverty threshold), or if the veteran maintains substantially gainful employment (exceeds the poverty threshold) and the VA determines that the rating is appropriate. The bill prescribes what disabilities may be considered as one disability (e.g., disabilities incurred or aggravated as a prisoner of war). The VA may not consider the age of a veteran or eligibility for retirement benefits when making any determination related to disability rating.