How did scholars classify bank funds under the category of usury (riba), and what is their evidence for that, and is there any disagreement among them on this matter?

The reality of how a usurious bank operates is trading in debts. It is indebted to depositors and a creditor to borrowers. It takes interest from them and gives them interest, and it gives to others and takes higher interest from them. It does not engage in buying and selling except within very narrow limits. All transactions of a usurious bank are overt usurious loan transactions, whether they are investment certificates, stocks, or bonds. The principle underlying all transactions of usurious banks is borrowing and lending with interest.