Maybe we're just at the natural equilibrium of the capacity of the planet given all extenuating factors, and with enhanced technology or interplanetary travel, we'll exceed those.
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.
There's literally gigantic websites showing how to fix the major underpopulation problems. Unfortunately if you're on say reddit or meta, their censorship disallows you to see the fixes. This is all political.
>And to make things worse, the trend toward lower fertility rates doesn’t seem to have any bottom.
There's now a huge political movement in the USA who are unhappy with Trump winning and are now swearing off sex for the next 4 years. Whatcha think that's going to do to fertility? You think its bad now...
>As things stand today, no one on the entire planet knows how to stop this trend.
You're up against the above political movement who arent going anywhere.
The reason 'no one' knows how to fix it is because it's not fixable unless you deal in politics. Which if you are on the 1 side of politics, you dont even know whats wrong. If you're on the otherside, you're dominating in politics because you know the fix.
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.