Greater wealth seems to also have discourage people from having children if the birth rates in wester countries are any indication.
I think we can do more to tackle the specific problems you mention through regulation and better policy, whereas a falling global population on its own would do little or nothing to combat them.
It is reasonable to expect growth rate will decline. Right now a billion people is predicted to be added every ~13 years. Even if the growth rate declines, population cannot continue to grow forever.
Ocean acidification from CO2 absorption, plastic pollution (including microplastics), overfishing, the destruction of the species that influence the oceanic carbon cycle and the overall increasing frequency of harmful algal blooms...
Not a good forecast for the continued survival of fish.
The limit will not only be because of CO2. There are other situations that need to be managed.
Population is increasing, and the lifestyle of individuals is rising, making each person have a larger cost on the environment.
Topsoil, the soil we grow our food in, takes long to regenerate and we are depleting it faster than it regenerates.
Overfishing cannot be stopped. Fish will be gone soon, and we largely depend on it. Fish as food, fishmeal for animals and fish oil as fertilizer (fish emulsion).