Benji, you're a bright guy, but you don't have this correct.
They are insolvent. The fact they can print money means they can avoid insolvency until they cannot print anymore. There is a point at which no one wants the 100 trillionth US dollar and then printing becomes futile.
The US is already buying its own bonds, which is indicative of a soft market.
You're not seeing that yet. Yet is the operative word.
That is only true if interest rates stay low. They can't stay low forever without completely destroying the economy and certainly, interest rates are manipulated by, but not totally set by the FED.
No one expects 1% interest rates to continue for any amount of time. Once the rate rises to 4 or 5%, shit starts to get real.
I suspect you're old enough to remember the 18% interest rates we had in the 80s that cleaned up the profligate spending and money printing of the 60s and 70s.
When that happened, the US was the world's largest creditor. Today, the US is the world's largest debtor. It will be a very different outcome.
What goes up, must come down.