You’re the one who said “if we can’t pay our debts we can’t trade.” That’s nonsense on its face. You need to explain that to me.

Meanwhile, I’ll waste cycles attempting to explain modern monetary theory on a phone keyboard.

Fiat currency is just numbers. Ones and zeros. The Fed(eral Reserve) can simply type these numbers into existence. That’s where the currency comes from. China can buy treasuries, but in a fiat system it’s unnecessary. Money comes from The Fed. The government could close the bond window tomorrow and it would just mean China would put its money in a bank account. Or, you know, spend it on things sold in dollars. Which is what currency issuance for.

Treasuries are a relic of the gold standard when currency was federally required to be tied to some quantity of shiny rocks. It was discarded because it artificially constrained monetary policy. E.g. during wars, the government couldn’t legally print currency, which is why there were all those silly war bonds.

Now the only constraint on issuing currency (really) is inflation. As we are about to find out, inflation is more than just currency issuance. Oil shocks, pandemic-induced supply chain crunches, and avian influenza outbreaks can raise inflation without any change in currency supply.