Whether that is healthy or unhealthy, the Fed can't be considered insolvent, they can literally create money.
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.