Spectrum IT Modernization Act of 2020 This bill requires the National Telecommunications and Information Administration (NTIA) and certain other federal agencies to outline plans for modernizing the information technology infrastructure used for the management of federal spectrum. Specifically, the NTIA shall identify a process to establish goals, including parameters to measure the achievement of those goals, for the modernization of such infrastructure and submit to Congress a modernization plan. The bill requires each agency to submit to the NTIA and the Policy and Plans Steering Group a report that describes the agency's plan to modernize its federal spectrum infrastructure so that such infrastructure is interoperable with that of the NTIA. The Government Accountability Office shall review the federal spectrum infrastructure of agencies and oversee the implementation of the modernization plans.