Nobody knows how to stop humanity from shrinking

Agree. This seems like a problem invented by business elites and economists, and propagated with the help of the media, to justify more consumption. They are not going to be affected by overstrained systems due to too many people. They don't want to pay the higher taxes to fund the infrastructure to support more people; they just want the top-line profits from more consumption and higher social status of having more people relative to their own high status.

Nah, what you're missing, at least in the U.S., is that the last 100 years or so have basically been a gigantic society scaled, Ponzi experiment w.r.t. things like Social Security. The entire system works, as long as population growth remains positive. Number must go up. The new revenue pays for people already drawing against the system. If things hit an equilibrium or, heaven forbid, start to shrink, the entire social order will start to break down ws the few social safety nets that exist start collapsing under their own weight. Remember, there's a constant handoff of amount of work to be done between generations at any one time. Once an overall smaller generation occurs, we either A)we have tech advanced far enough where some of the work to be done can be handled by fewer people, or B) start seeing the work deemed necessary to do get done get forcibly trimmed down by virtue of simply not having anyone to do it. Trajectory is suggesting we're banking on A, but we're also not focusing on making sure that we can pull it off without mentally mulching the people doing all that work.

Immigration and taxation can stall having to come to terms with this for a nation for a short time. However, there is a fundamental breaking point for humanity on Earth as a whole where all polities will be in the same boat.

Revise systems to get sustainable, stopping the chasing of unsustainable, unbounded growth while we figure out how to decrease the overall resorce pressure, or watch everything crumble as the entire thing falls apart under it's own weight. Those are the choices. Watch international violence spike back up as a relief valve to decrease the population pressure.

Oh, and in case you're wondering, no, your QoL/SoL won't "go up" most likely peeps in the west. It'll likely regress to the mean of everyone else; because that reaource footprint that's buoyed things thusfar was the result of being the industrial and economic superpower coming out of the last series of global conflicts.

What do I know though. I've just worked on the clusterfuck that is the U.S's last gasp at international relevance, and personally witnessed the throwing out of the baby with the bathwater in the name of the self-enrichment of the few for the last half of an average human lifespan.

The spirit of our times is not in an overall good spot.

The idea that slowing population growth is a problem, in need of a fix, is itself a political position. From another point of view, this is a good thing, which will be part of a fix for other problems.

The 4B movement isn't "huge". That, too, is media manufactured.

But yes, people are definitely going to have even fewer children if the country is going to be so malignant. You can have lots and lots of sex without having any children.