TRICARE Retiree Protection Act This bill authorizes a covered beneficiary who is enrolled in TRICARE Select to reenroll in TRICARE Select at any time during 2021. Covered beneficiaries are those in the retired category who (1) enrolled in TRICARE Select as of December 31, 2020, (2) did not establish a monthly enrollment fee payment during the 2020 TRICARE Open Season, and (3) submit an assertion that they did not receive notice regarding the process to enroll in and establish a monthly enrollment fee payment for TRICARE Select for 2021. A covered beneficiary who reenrolls in TRICARE Select must, at the time of enrollment, pay a portion of the annual enrollment fee and establish a monthly enrollment fee payment for the remaining months of 2021.