Define collapse. The world population is on track to start declining starting in the next few decades. However with 8-9 billion humans how large a loss would you require before you call it a collapse is a debatable question.

Increase in global population will continue for a few decades, but there are more old people than young people and it seems unlikely that we will get to a phase where births are high enough to counteract coming the death by old age in the near future.

I believe this is a good thing even if it will cause many issues. Humanity will have to live on earth for a long time and infinite growth is not sustainable. So at some point the population has to fluctuate. We will have to accept this reality.