“Of course all the responsibility for US currency belongs Constitutionally to the Congress”
Sounds like someone is confused. The Constitution is notably silent on currency. It does grant Congress the authority to mint coins.
Private banks printed their own currency all through the 19th century. Sometimes they were required to hold gov’t bonds to back their currency, sometimes they weren’t.
Banks in fact still have the legal right to issue their own currency. It costs them to do it, whereas creating money via ledger entries on checking accounts doesn’t, so no one does.
a good short description of Money & the Constitution is found here:
https://billofrightsinstitute.org/money-and-the-constitution/
I believe the Treasury does still create the coinage.