Make people wealthy and the birth rate goes down. Can be done if we can be bothered, and people will bother us to.
If you are talking about individuals that is only true to a certain extent, when societies are moving (or have recently moved from) states of high infant mortality. In countries where child mortality has not been a major concern for a long time, wealthy people have more children because they can afford them.
Or maybe when you say ”make people wealthy” you mean societies as a whole, i.e. industrialization? Then that is true, because industrialization causes that shift from high natality+mortality to low natality+mortality. This is known as the
demographic transition(though if this was your point you might have known this already). Though populations may stabilize on the other side of it (or not, see Japan, Italy), so it is not a guarantee for lower populations, rather the new stable population will inevitably be higher than the one before. In fact, this is the main reason why concerns about ”over-population” on a global scales are icky - because the parts of the world with rapidly increasing populations (mainly Africa) are those that are going through the demographic transition due to their economic growth. This is not a new development, it happened in Europe and the US as early as the first half of the 1900s, and now the global late comers are catching up. To then complain about ”over-population” as a person in one of those countries which has already seen its explosion in population growth (goes for me, and I assume most members of this forum, due to literacy numbers and English), just isn’t fair, and that’s foregoing asking questions about ethnicity of transition/post-transition states and why these states are late to the scene.
To make it clear, I do not think we need to worry about over-population. I think we need to worry about the climate and consumption, and that is of course connected to the amount of humans consuming, but the populations themselves seem to stabilize at some point. Worrying too much about it now
could be racism, or at least ”let people of some other state deal with the climate crisis”-ism.