The Addiction Grants Modernization Act authorizes the Secretary of Health and Human Services to create a single, centralized online application system for federal substance use disorder grant programs across multiple agencies, including the Department of Health and Human Services, the Office of National Drug Control Policy, and the Department of Justice. The bill requires the secretary to identify which discretionary grant programs will be included in this system and establish a secure website interface where organizations can browse and apply for grants filtered by organization type and activity area such as prevention, overdose reversal, treatment, and recovery services. A working group composed of federal employees and non-federal stakeholders like state directors and community organizations will develop recommendations for the centralized application system and report to Congress by an unspecified deadline. The bill requires the secretary to publish the list of covered grant programs by December 31, 2028, and to synchronize funding announcements across programs whenever possible, though it does not authorize changes to existing grant funding levels or eligible activities.