State, Local, Tribal, and Territorial Fiscal Recovery, Infrastructure, and Disaster Relief Flexibility Act This bill allows states, tribes, territories, and localities to use certain COVID-19 relief funds for new categories of spending, including for natural disasters and infrastructure projects. It also makes changes to expenditure deadlines and other aspects of this funding. Specifically, recipients may use funds for emergency relief from natural disasters and associated negative economic impacts of natural disasters. In addition, recipients may use a portion of their COVID-19 relief funds for designated infrastructure projects, such as nationally significant freight and highway projects. Furthermore, the bill allows recipients to expend COVID-19 relief funds on these types of infrastructure projects until September 30, 2026. Under current law, recipients must expend the funds by December 31, 2024. Other changes in the bill include (1) modifying eligibility and allocation requirements for funding set aside for counties and Indian tribes that are near public lands, (2) allowing Indian tribes an additional year to expend their COVID-19 relief funds, and (3) establishing a process for government entities to decline COVID-19 relief funds and requiring any declined funds to be used to reduce the federal deficit.