This is not exactly right. True, $8B is not earth shattering because of the US's enormous debt. But by removing a potential $8B owner, it is a reduction in demand, and thus a tiny reduction in price. This is literally the first rule of pricing: "supply and demand".

Sure, someone else is on the other side of the deal. But their demand is also satiated at a certain price point. Hell, if they wanted to buy from other sellers then it's not like T bills were not liquid.

Would you say the same if Norway's wealth fund offloaded their $181B? At those scales it would be more likely that it'd be visibly price affecting, and therefore affect the US's ability to borrow at existing cost.

So yes, when you sell your one NVDA, you are reducing demand and thus price. Epsilon, but nonzero.