Nvidia casually fell 9.27% or $280B on the first trading day of September for no reason

The reason turns out to be. After the close of trading - the company announced it had received a subpoena from the US Department of Justice related to an antitrust investigation into Nvidia's position in the AI industry.

What kind of Polichinel secret is this if the market was falling behind this subpoena in advance without knowledge of its delivery?