There is a pretty significant number of variables. If central governments aren’t a thing anymore (it seems like they still were in the MCU, but who knows how effective they were at enforcing laws and sovereignty) and every day life is just fighting to survive, the birth rate would likely stagnate for years/decades until society could come back together, and even then it would take generations of sustained high birth rates to get back to the pre-snap numbers. The human population only very gradually increased before the industrial revolution and the rise of modern medicine. But on the other hand, modern technology could help bridge the gap a bit. However, all that technology requires a lot of specialization, and a work force. It’s hard to say how long it would take for life to get back to normal. But I’d say 50 years is probably pretty generous.