In 1980, Japan had a huge population boom in the 35-45 age range, of energetic people who had grown up during a golden age of technological and economic development. Then they were hit by a demographic timebomb...
https://www.nippon.com/en/in-depth/a01001/
By 2060 Japanese children will be in the low single-digit millions, maybe 1/3 of the number when the experienced workers of the 80s were kids in the 1960s. There is literally nothing that can prevent it except mass immigration on a scale that would totally transform Japanese society (and which consequently will never happen).