So is this a trick question? A multiple choice question? Why did I waste my time searching for the answer only to be told we don’t know. We didn’t try to estimate the number.
50 sq miles per person is an absurdly high figure, except for the Sahara or other desert region.
Tribes of the Americas were mostly semi-nomadic at most, with plenty of longer term settlements and lots of settled agricultural populations.
The rises and falls in Precolumbian populations have long been understood, this study appears to be expressed a percentages. I couldn’t find a complete PDF, just the abstract.
https://www.pnas.org/doi/10.1073/pnas.2419454122#abstract
https://www.pnas.org/doi/10.1073/pnas.2419454122