The proper way to refer to the indigenous peoples of the America is honestly a pretty complicated topic. "American Indian" is still generally considered valid. In some cases it may even be more correct, like when referring to indigenous peoples from outside the modern United States. It's typically preferable to name specific groups though, as indigenous peoples weren't homogenous. Just "Indian" is pretty outdated, but you'll occasionally see it on things with a lot of historical baggage, like the BIA.