@JeffC1956 Most regional human populations on this planet are already shrinking, the overall still positive growth rate is falling, and the human population peak is expected not to exceed ten billion humans. Unfortunately, I think human population might peak much earlier when one of the most densely populated regions, South Asia, gets hit with deadly wetbulb temperatures again and again, killing tens of millions within weeks year after year. Failing crops due to all that climate chaos will probably cause famines, we might reach the first global famine where there actually won't be enough food for all humans, even if it were distributed equally, within less than a decade.
What we need now is quite the opposite of all the nationalism we see all over the planet. Nations aren't real, we invented them, and the only way we can make them real is by drawing their borders on the actual soil with human blood, again and again. When billions of people lose their homes (which is a thing that _will_ happen, no matter what we do, because the damage we have already caused will continue to eat its way through the Earth's systems ), they will need a new place to live. All these nations and their peoples that we see today will be remixed into new ones, there is nothing any nationalists or racists can do to stop that from happening, but those that are trying to stop it will murder billions if we don't stop them first. It doesn't matter if my nation doesn't exist anymore in 200 years, nations and cultures come and go as the millennia go by; it doesn't matter if there aren't any "white" people anymore in a few generations, what matters is that enough of our species survive to carry on evolving.
Don't worry about how to shrink our population, but fight for women's rights everywhere on this planet. As soon as women can decide whether they want children or not, many just don't have any. Since not every woman wants to be a mother and most mothers are fine with just one child, cutting human population in half with each generation would be quite feasible. Unfortunately, all kinds of catastrophes will very likely shrink our numbers much faster. If I could live to see it happen, I wouldn't be surprised if there were only 2-4 billion humans left by the end of the century, and less than a million by the year 3000, but that would still be more than enough to save our species, even if we might never have a complex civilisation again and would spend the next million years in tribal societies. Eventually, the Earth will heal, the climate will be stable enough (even if very much hotter), and if we don't go extinct, we'll evolve into the next hominid species after Homo sapiens, physically adapted to a much hotter planet, and possibly able to start another Neolithic Revolution. Probably no Bronze Age or Iron Age again because we depleted the ore deposits, those will take much longer times to replenish, the genus Homo will be long gone by then.
Eventually, our entire genus will go extinct, even if we Homo sapiens manage to survive the Sixth Extinction, which has only just begun and will probably go on for at least a few thousand years after the collapse of the Industrial Age. Everything dies eventually. If some strange posthominid creatures manage to survive long enough, they will die when our sun starts burning too my hydrogen, getting bigger and bigger; at some point a bit over a billion years in the future, the Earth will become too hot for anything but extremophile microbes, and a billion years or two later, everything will be sterile and dead.