The Nikkei article that reported 35,000 Z9 cameras monthly production has a typo: they added an extra zero to the original number reported by Nikon in a press release – the monthly Nikon Z9 production is actually 3,500 cameras (the Nikkei article is still not updated with the correct number):
This probably also means that the total number of Z9 pre-orders is 40k and not 400k as reported by Chinese social media.