Offer education, contraception, and healthcare universally, regardless of border. This would tank the birthrate in a non fascist way, which is an objectively good thing. This weird procapitalist idea that we need or should want or really could sustain 8+ billion apex predators is ridiculous. In no ecosystem is that sustainable, even if the predators are smart enough to stop directly predating in other animals.

We should genuinely be striving for the least number of people that still allows the highest quality of life, with a further constraint being the lowest impact to the rest of the environment. Make no mistake, everyone regardless of immutable or even mutable status should be allowed to have kids if they want, but we shouldn't want or need to frame it as something essential to continue continuity of wage labor.