I always found this argument quite flawed. In developing countries with much worse conditions people continue to have kids. It is all about our values and the incorporation of women to the labour force. In my circles that's the predominant cause: women first want to prioritize their careers before having kids, therefore they postpone it which inevitably leads to lower birth rates.

The proof is also that this happens all across Europe and Western world, but there are countries like Switzerland where young people are doing just fine and have high salaries and low unemployment. And birth rates are not significantly higher.

Therefore, even if the situation improves, expect birth rates to remain stagnant. That is the price for women prioritizing their careers and modern feminism's push to undermine their function as nurturers and carers. I am not saying women should not have a good career, I am saying society should value much more the act of forming a family and raising the next generation, and not so much just materialistically having the best career path.