“Number of humans” is a nonsensical metric because it doesn’t acknowledge the systems that humans comprise. For example, we depend on the young to earn/work and the middle aged to earn/work/invest to support the old/disabled. What happens when there are fewer young people, and then fewer middle aged people, to support the old /disabled not in just a few pockets of the world but in many countries all at once is still very much unknown.

It’s not the number of humans, it’s the age distribution of those humans + where they live.

Put another way: you can “feel” like the world needs fewer people, but you’re probably not going to like what your world looks like when that desire comes true.