TL;DR The estimate of 8 billions humans on Earth might be underestimated. Because in specific areas where a dam is built and relocated population is precisely counted, they realized that they were underestimated.
But this is just one publication that does not convince other scientists that the estimation would be too way off. So until further notice were still 8 billions.
You make me want to watch Fraggle Rock again. Apparently it's on Apple TV+ and they made new seasons. Or, you can find it the other way...