Student Mental Health Helpline Act of 2021 This bill authorizes grants to support student mental health and safety helplines (i.e., a free, confidential service that is accessible via telephone and other communication platforms that assists students facing challenges with abuse, bullying, depression, self-harm, and related issues). The Substance Abuse and Mental Health Services Administration (SAMHSA) may award the grants to agencies or other subdivisions of a state, Indian tribe, or local government that are primarily responsible for health, public health, or education. Among other purposes, recipients must use funds to establish or maintain a helpline that provides information to school officials (to the extent permitted by federal privacy standards for health information) about student mental health and safety concerns. The bill also requires SAMHSA to report on the feasibility of setting up a nationally available student mental health and safety helpline.