I believe that in case of population collapse, the solution will naturally appear to large enough number of people, evolution shaped us to reproduce, I don't think this instinct is likely to disappear, even if we might not fully understand it and why girls and women tend to have less children in some conditions (it happened before, in antiquity, and was considered to be a problem by Roman politicians, many of the current traditions around marriages were first created as laws...)
The solution evolution found was to make us really like having sex. But then we invented hormonal birth control, and sex became uncoupled from reproduction. Evolution can't help us here, it works slowly over thousands of years, and can't uninvent birth control.
This isn't always the case; evolution can happen relatively quickly in response to rapid changes in the environment [1]. There are plenty of people alive today who have particularly strong urges to have children, and the widespread introduction of birth control creates a major selective pressure towards any heritable genes that produce or enhance those urges. The effects of this could be very significant over even a relatively small number of generations.
Housing policy, tax policy, education policy, healthcare policy, family law - governments are influencing population massively.
Economic problems are real and worth addressing and I hope we can find ways other than “we need more babies”.