Malthusianism isn't real. Demographics are.

We can build more housing, grow more food, etc. There is no real concern of hitting a numerical upper limit in the population we can support. What matters is "can we provide for everyone at this moment".

For China, rapid population growth would have been an enormous resource strain they couldn't afford at the time. Limiting births reduced population growth, but it also reduced the size of young generations. China now has a large population that will one day retire, leaving a disproportionately small workforce. This will make it hard to support them. Not too many people, but too few.

This problem has already occured in some Western nations. Here it wasn't state enforced policy, but more "natural" changes in demographics. It's overburdening the what Welfare systems do exist.

Reducing the workforce is not how we reinvent the nation along sustainable lines of development. That's actually going to take a lot of work. What will get us out of this climate crisis isn't the individual decision or compulsion to consume and do less, but a restructuring of our society.