To my knowledge, nobody in the investor community considers US govt default a realistic risk.

The problem the US faces is if the interest rate on their bonds goes up, it causes a global bank run on all banks. You see, nobody will leave cash in the bank at 0.2% when they can lend to uncle sam at 10%, and the banks can only pay 0.2% because they used that cash to write 30 year mortgages at 1% back in 2017, so boom the whole banking sector suddenly becomes insolvent.

> on the long term (centuries)

Nobody holds cash for centuries because over such a long timeline it gets devalued to nothing.