Stop Fentanyl Overdoses Act of 2023 This bill establishes several programs and requirements to address the use of fentanyl and related substances, including public health programs and programs to support law enforcement activities. For example, the bill requires federal agencies to prioritize data collection and reporting about fentanyl in existing drug surveillance programs, such as the Centers for Disease Control and Prevention's Overdose Data to Action program. It also establishes training and grant programs to support state and local agencies with fentanyl detection and tracking. The bill also requires the Department of State to report on countries that are the principal sources of synthetic drugs trafficked in the United States, and it requires the Government Accountability Office to report on the impact of the Drug Enforcement Administration's High Intensity Drug Trafficking Areas program on illicit fentanyl that is imported via mail and cargo. The bill also establishes programs to support education and treatment relating to opioid use, including a grant program for state and local agencies to provide educational resources and a program to provide treatment in federal prisons. It also provides immunity from civil and criminal liability for those who administer opioid overdose reversal drugs (e.g., naloxone).