The world is overpopulated, but it's simplistic to say that it's the be all and end all of the world's ecological crises. There's a formula that goes I=PAT, or "Impact = Population x Affluence X Technology." So, for instance, China has more GHG emissions than the US, but the US has more GHG emissions per capita. India comes in at #3, but the US has 8x more GHG emissions per capita than India.
So, overpopulation is a problem, but it's a problem that's as much an issue in the developed world as the developing world. To reduce impact, we need to reduce population, affluence, and/or technology. Or, ideally, all three. Best case scenario is a world with as few people as possible, living the best lives possible, with minimal impact.
I've seen lots of predictions for the future of human population, ranging from figures as high as 16 billion by the end of the century to the idea of a population crash beginning by mid-century. A number of countries are shrinking, while various African nations have exceptionally high fertility rates (e.g. Nigeria). What worries me in a sense is that the question of whether the world can sustain so many humans ignores that there's no such thing as a free lunch. If the world has that many humans, the rest of Earth's biosphere can't help but suffer as a result. So when people lament falling fertility rates in the developed world, I can only say "good." Because whatever short-term economic hardship a shrinking population has for a country, it's preferable to long-term ecological destruction.
In essence, consumption and population need to be reduced hand in hand. If everyone on the planet had the same standard of living as the US, we'd need three Earths to support it. If we want everyone to have that standard of living, then it's been calculated that the world population couldn't exceed 2 billion. Frankly, I have little hope considering that not only do we need to reach net zero emissions, but have to go carbon negative as well to avoid catostrophic climate impacts. And that's in addition to a rising population, plus rising standards of living, plus rising emissions. We're headed to the cliff, and all we've done so far is tap our foot against the brake.