I recall reading, a long time ago, of a person who was eating just meat and only meat for his diet. He was struggling for a while with it, until he intentionally allowed a small amount of meat to rot for a bit, consumed that, and from then on he did much better on that diet. The principle I believe was in play was that the rotting meat contained a lot of bacteria that was very good at breaking down that meat (it would proliferate the fastest) and that bacteria was taking up residence in his gut microbiome and assisting in digesting non-rotten meat in the future. Sort of like how herbivores will sometimes consume small stones to act as mechanical grinders of plantstuff in their stomachs.

This seems like the most likely way that ancient humans consumed actually-rotten meat, in small doses to edit their gut microbiome (likely encoded in traditions that viewed certain specific rotted foods as a delicacy/luxury - not because it was hard to acquire but because you were only supposed to eat it rarely). To the extent that you see claims that “ancient humans ate large amounts of rotten meat” I suspect they’re conflating that with merely “spoiled by modern food standards” meat, which is much less rotten than it sounds.