100 million people scattered all over North America isn’t actually much, it’s a big 3 countries with a LOT of fertile land and tons of animals.
It’s roughly 100 times more than a stone age culture could support, and there is absolutely no evidence for it. The “high count” claims are no better than afro-centric “history” that claims that Cleopatra was black and that 60 million blacks died and were thrown into the Atlantic in the middle passage, which accounts for sharks today still swimming the slave trade routes. It’s all rubbish that credulous conservatives will buy if they see it on a cable channel and run into it enough in print.