Might as well say it: 8 billion is too many, and it’s a good thing that population growth is levelling off. A decline down to ~1 billion would be fine. If we have to change retirement planning, so be it. No other species can grow its population exponentially indefinitely. Population growth in every other species is kept in check by conflict and starvation. We have an opportunity to voluntarily limit our footprint to…
Every generation has it's soothsayers that are absolutely certain we are near the population limit and heading for certain doom. And every one of them was wrong. Our population soared past those limits, no problem.
I share the opinion that earth can sustain about 100B of us, with a bit of planning and thoughtful engineering. So long as most people don't mind living in sky scrapers. More people = more brains to solve the type of problems that I assume you are worried about.
I don't actually believe we will continue growing like we have, as nothing in human affairs follows a strait line for long. Every great kingdom has fallen, every empire divided. It is ebb and flow, tidal gravity. We don't need to try and control it, but only observe and adapt to it.