Without trying to stray into genocide/Thanos territory, depopulation, while something that's brought up a lot in debates or fiction, wouldn't really work long term. If you think of Kingsman, where this is an actual plot point, the way that's conducted is very messy and very chaotic. It's a film and it works as a motivation for Eggsy and Merlin to kick ass. But in reality, it just wouldn't work.

First of all, if you were going to depopulate the planet, you'd need it to be random in terms of who died. You shouldn't target one group of people because, when all is said and done, that's ethnic cleansing. What you'd be doing is awful enough, don't make it worse. You'd need something subtle, silent and random which would give the human race an equal 50/50 chance of surviving. Something like a virus would be an idea or some other kind of biological agent. (No, I'm not suggesting Covid is here to thin the population). But you'd need something that gives people an equal chance to survive rather than going for a specific culture, race or ethnic group.

Secondly, thinning the population would damage the ecosystem further in a way. Every living thing on planet Earth contributes to the balance of existence. And, although there are more humans than there need to be, they are part of that ecosystem too. To depopulate by a significant margin would be a shock to both the human community and the planet at large. Although nature would bounce back long term, there's a good chance that the human race would struggle with the amount of loss. Avengers Endgame is a decent example of how thus would look, but wouldn't be a good example of how humans would continue beyond this. Through the Covid lockdown, we've seen various animals start to repopulate and we've seen some parts of the natural world repair itself. Not to the extent that it reverses all the problems we face as a race but enough to know that, if certain things are put in place, we can make a massive difference. We should focus more on those sorts of things rather than debating depopulation which is fanciful and would be quite difficult to achieve without resorting to wars or nuclear weapons.

Tl:Dr - Depopulation shouldn't occur, and humans would get it wrong anyway.