Given current technology, what is the maximum sustainable human population of earth?
I don’t think there’s even a tiny chance you’ll get a factual answer for this question. You might want to ask a mod to move it to IMHO or Great Debates. But in the meantime, I’d search the latter forum for previous discussions of population to see what’s already been said.
Such as 6 billion? (It ain’t pretty; don’t say you haven’t been warned.) Most of the technical information is around pages 3, 4, and 5.