I believe there were maybe 10 million total of all native Americans in what is now the US and Canada. No census was ever taken, but no large settlements of any size like a city were evident in the North American continent at the time of Columbus up until the Pilgrims. Had there been anywhere near 90 million, history would have been much different........
I have seen estimates from 500,000 to several million. 10 million doesn’t sound too off the the charts. But, bear in mind that the population of England and Wales, at the time of the census of 1801, was only 8.9 million; and, they had metal tools and work animals. People have no idea how hard life was before the industrial revolution in Europe; nor, how much harder is was before the discovery of metal working and the domestication of work animals.
Survivors of de Soto's expedition along the Mississippi river in the early 1540's described towns with hundreds of buildings connected to other towns by systems of roads and trails. One hundred years later, the next Europeans to explore that area only found isolated villages.