Supplemental Security Income Restoration Act of 2021 This bill modifies eligibility for, and other components of, the Supplemental Security Income (SSI) program, including by (1) increasing applicable income and resource limits used to determine SSI eligibility, (2) equalizing treatment of married couples when both spouses receive SSI as compared to two unmarried individuals, and (3) eliminating the penalty on SSI applicants or recipients who transfer resources to another individual for less than fair market value.