Alan Weisman's book Countdown revealed to me about countries that lowered birth rates without coercion. Before reading it I only know about the one-child policy and some eugenics attempts. I highly recommend the book. I just recorded a conversation with him for my podcast. Fascinating conversation but it's still in the editing queue.

Off the top of my head, his main examples were Thailand, Iran, and Mexico. Here's a piece on Thailand https://www.context.org/iclib/ic31/frazer. Wikipedia covers Iran between 1989 and 2006 https://en.wikipedia.org/wiki/Family_planning_in_Iran. Cultures including Japan and Italy saw dramatic decreases in birthrates without focused efforts.

Here are videos of him: https://www.youtube.com/results?search_query=alan+weisman&oq.... I haven't watched them, but probably will give you a jump start on the book.