No I would assume that at the margin, increases in population are drastically skewed towards more poverty.

So if we we went from 8B to 80B I'd argue we'd go from 1B -> >50B in poverty. Maybe a lot worse than that.

This is obviously dependent on where you are born but especially true once you consider that the places left with high fertility have nearly perfect overlap with the places with high volumes of extreme poverty.

And this is only in the short term. Those people are generating plastic waste, consuming fuel, and many other things that are net negatives to the planet over time. So over the long term this problem just gets worse.