You are claiming it is backed by nothing. That is untrue.
To start, understand reserves. They are not legal tender. They are simply bank instruments that have a specific use case. They are not broad economy money. They cannot be used for another but interbank settlement.
As stated, all deposits (liabilities on a commercial banks balance sheet) are backed with either government approved assets (US treasuries or MBS) or notes from loans.
I'm not claiming anything that the Federal Reserve itself is not claiming.
ZERO reserves since 2020.