Safeguard Tribal Objects of Patrimony Act of 2021 This act prohibits the exportation of Native American cultural items and archaeological resources that were illegally obtained; provides for the return of such items, including voluntary returns; and establishes and increases related criminal penalties. Specifically, the act makes it a federal crime to export, attempt to export, or otherwise transport from the United States Native American cultural items and archaeological resources without obtaining an export certification. U.S. Customs and Border Protection must detain any item requiring an export certification that does not have one. The act requires the Department of the Interior and the Department of State to each designate a liaison to facilitate and hold trainings and workshops on the voluntary return of human remains and cultural items. Additionally, Interior must refer individuals and organizations to Indian tribes and Native Hawaiian organizations to facilitate the voluntary return of human remains and cultural items; convene an interagency working group; and convene a Native working group consisting of representatives of Indian tribes and Native Hawaiian organizations to provide advice on issues concerning the return of, and illegal trade in, human remains and cultural items. The act also increases the maximum criminal penalties for violating the Native American Graves Protection and Repatriation Act. In particular, the act increases from 5 years to 10 years the maximum prison term for an individual convicted of a second or subsequent violation of selling, purchasing, using for profit, or transporting for sale or profit human remains or cultural items that were illegally obtained.