Low fertility, as well as high abortion rates, and bad mating and parenting choices, can be fixed for free: give back the return on investment for raising prosperous children to the rightful recipients. Give parents all the socialist security related deductions from their children’s future paychecks. That is functionally how it worked throughout most of history, and still does in most of the world.
“Doomsayers such as Elon Musk warn that these shifts threaten civilization itself. That is ridiculous,”
It is not ridiculous unless you think we can have civilization without humans.