Banks practicing FRBs have liquidity reserve limits, and are frequently audited, and have to be solvent (Value of all assets minus liabilities exceeds value of all deposits) in order to operate.

Tether is a fly-by-night con job that, to disburse USD redemptions, wires hundreds of millions of dollars to money launderers in the Carribean, who then go ahead and steal most of it.

And when law enforcement starts digging through their books, we discover that a third of Tether's 'reserves' consist of a "I'll pay you guys a few billion dollars, pinky swear", scrawled on a napkin.

It's not fractional reserve. It's straight-up fraud.