Don’t have one. Not all pensions are pyramid schemes.

Further, flat growth would be acceptable if that is your primary concern.

Genuine question - what is your retirement plan? I have seriously looked and didn't find one yet which doesn't need population growth and/or productivity growth.

My personal plan, or one for everyone?

I don’t have a pension. I do have a 401k/ira, and would prefer my social security taxes were in there as well.

Lower population would help the housing crisis, which is a huge tax on everyone. Own a home and a garden.

One way or another there is

https://en.wikipedia.org/wiki/Dependency_ratio

and it affects all the ways you might retire, no matter if it is "my children will take care of me", "my government will take care of me", "my mutual funds will take care of me".

The situation gets more favorable with more population/economic growth, is difficult in the steady state, and is atrocious in a state of decline. See

https://en.wikipedia.org/wiki/Logan%27s_Run_(film)

Flat population would be fine with me, declining population makes many things unmanageable as would a rapidly increasing population.

Fortunately there's no risk of declining population, except in rare/brief circumstances. Why alarmism over falling birthrates is misplaced.