I think the lower birth rate can be several things.

1. Low sperm counts due to microplastics.
2. Too much suffering and environmental abuse in general causes mother nature to fight back (leading to things like #1)
3. People have poor outlooks on the state of affairs and feel having children is irresponsible
4. Most can not afford it
5. Isolation caused by dopamine addiction from tech
6. Isoation caused by political division (USA, EU, Canada)
7. Isolation caused by shame and working too much (Japan)
8. People work too much and don't have time for kids
9. People don't have whole communities with warm relationships any longer causing parents to have the whole load in an untrustworthy world
10. Many people just hate being around kids or simply don't want them

Oxytocin is not the answer. The answer is fair wages, health care, decent and affordable education, homes that are affordable, no private equity in healthcare/education/residential real estate, telework flexibility when available, waste reduction and removal, third places other than churches and outdoor parks that are cold in winter, healthy food, and personal limits on screen time.