have you ever asked them? My wife works on reservations. They unanimously want to be called Indian. CGP Grey has a video on it as well I’m pretty sure. And I think it’s pretty telling that the agency is called the Bureau of Indian Affairs and not the Bureau of Native American affairs. www.usa.gov/agencies/bureau-of-indian-affairs
We’ve had plenty of reform of sports team names, you’d think they’d want to reform the actual federal agency name if it wasn’t what they wanted it to be called.