500 million people:

https://welovetrump.com/2020/08/19/the-creepiest-american-monument-youve-probably-never-heard-of-the-georgia-guidestones/

I think if global overpopulation is a legitimate concern, then space exploration/colonization is a better solution. Aliens not wanting humanity to rise up as an independent power would be against this. This is probably why MSM ridiculed Space Force and why we have flat earth shill spamming.