Recent works on Indigenous societies in North America suggest that populations could have been as high as 120 million across the continent. Societies in central and south America would have likely centered around metropole style cities.

Indigenous land-use and ecological impact could have been much higher as well. A study done on florae along the east coast suggests that European explorers recorded the presence of a particular form of florae that only grows out of burnt wood and charcoal, suggesting large amounts of terraformation (burning unecessarily) to make space for farmland.

Our understanding of a vaste empty expanse usually comes from a) accounts written long after first contact, usually during the 16th/17th c., after the Indigenous population had been reduced to 10-20% of its original size due to European diseases and b) interpretations of indigenous societies from the 18th/19th c., largely based on those few accounts. It has taken longer for archeological hypotheses and oral histories to become valid source material (and still often isnt).

Sources: William Denevan "The Pristine Myth: The Landscape of the Americas in 1492" Annals of the Association of American Geographers (1992) and Shephard Krech "Fire" in The Ecological Indian: Myth and History (1992).

EDIT: There is another book that was published recently that tackles this issue quite well and I wanted to cite, but I cant for the life of me remember the name. If anyone has any idea what book Im referring to it would be much appreciated.

EDIT 2: Added important part about death rates to disease being high, creating myth that land was always empty. Also, I typed this on my phone so it was riddled with spelling mistakes.