There's no population or fertility crisis. The world's population isn't going to fall, it'll level off around 2100, nobody old enough to read this will be around, our kids and grandkids can decide for themselves.

Local populations will see very different trajectories, yes. Africa will see population growth and many other places will see steep decline. Societies can choose to keep their current system and take in immigrants, or choose to keep their "national character" (or whatever) and rejig their societies so the remaining productive parts pay for increasing numbers of old people. Grifters (Brexiters, MAGA, Le Pen, etc) will attempt to sidestep such obvious tradeoffs, but they will fail, hastening the decline of these societies. So the only crisis we have is people refusing to deal with reality's tradeoffs.