Juvenile Incarceration Reduction Act of 2020 This bill limits the use of risk and needs assessment systems in decisions related to juveniles in a criminal law context. (A risk and needs assessment system evaluates, among other things, a particular individual's risk of recidivism after release from prison and what programs may reduce that risk.) Under the bill, such a system may not be used to determine whether a juvenile may or should be treated as an adult in a criminal proceeding. Such a system may also not be used (1) to determine the recidivism risk of a juvenile charged with a nonviolent offense, or (2) as the sole factor to determine the recidivism risk of a juvenile who has committed an act of juvenile delinquency that would be a felony if committed by an adult. The bill also prohibits using such a system to (1) determine a juvenile should be taken into custody for an alleged act of juvenile delinquency prior to adjudication; or (2) establish, without additional evidence, a juvenile's eligibility or suitability for a recidivism reduction program. If such a system is used to determine the recidivism risk of a juvenile who has committed an act of juvenile delinquency that would be a felony if committed by an adult, any evidence established by the system is inadmissible as evidence to establish that the juvenile committed the act in question.