I don't know if there's a specific trope name for when a group of people in media are 'coded' as Native Americans, I first noticed this in the depiction of the Great Khans in FNV, particularly in the character of Papa Khan and his manner of speaking, Another instance is in a DLC for the game Total War, where you play as the Nanman people who are portrayed as Native American-esque and I recall seeing a clip on YouTube (which I am currently unable to find) that depicted the Montagnard not only as Native Americans-likg but also featured Native American actors portraying them