Achieving Thorough Transparency and Accessibility for Information Navigation on Mental Health Act of 2021 or the ATTAIN Mental Health Act This bill requires the Department of Health and Human Services (HHS) to establish a public-facing, online dashboard to publicize federally funded mental health grants. The dashboard must contain, for example, program names and opening and closing dates for applications. In addition, HHS must establish a process to include information voluntarily provided by states about their federally supported mental health grants on the dashboard. In developing the dashboard, HHS must consult with appropriate federal departments and agencies and other stakeholders.