The ability to print up infinite amounts of notes doesn’t change the fact that they are insolvent when liabilities exceed assets. Every dollar that’s printed becomes both an asset (while they have physical possession) and a liability (responsibility to exchange note for money) on their balance sheet.
Now what changed in August 1971 “temporarily” was that they’d no longer exchange the Federal Reserve notes for money. Instead if a customer gives the Federal Reserve one of their notes back they get an electronic entry on their ledger that they have funds in the amount of that note in the system.
That wasn't your original definition.
not solvent; unable to satisfy creditors or discharge liabilities,
There were no liabilities that you listed that they cannot satisfy.
Their bond holding have dropped in value, obviously. Instead of turning over their annual profit to the US Treasury, they may have to retain it, against their unrealized losses. But there is no scenario I can see where a "creditor" comes to the Fed to get their money and the Fed is unable to give that creditor either FRNs or an electronic ledger entry.
Can you?