If we manage to stabilise world population at mid 70s level, it would be a great success TBH. Birth rate decline is accelerating and majority of population would be old people, who are able to work much less and require a lot more care, so the raw labour power would be much smaller. I bet all of the West would introduce euthanasia to deal with it.

Also, capitalism is working like shit, when the population is not growing, and if it begins to decline, it will crap itself much more than now, and it will accelerate decline even more, until this positive feedback results in either communism or agrarian traditionalism, and the latter currently seems more likely.