Especially in contemporary times banks make money in an immense amount of ways that don't involve touching customer funds: debit transaction fees, international exchange rate "adjustments", ATM fees, the million 'special processing fee' type fees, and so on. In other countries I've even had to pay a fee when depositing, which was quite odd.
Of course this all is going to pale in comparison to the amount that banks make by d̶u̶m̶p̶i̶n̶g̶ ̶c̶o̶n̶s̶u̶m̶e̶r̶ ̶f̶u̶n̶d̶s̶,̶ ̶h̶e̶a̶v̶i̶l̶y̶ ̶l̶e̶v̶e̶r̶a̶g̶e̶d̶,̶ ̶i̶n̶t̶o̶ ̶h̶i̶g̶h̶ ̶r̶i̶s̶k̶ ̶a̶s̶s̶e̶t̶s̶
responsibly investing deposits. But of course banks under '100% deposits maintained' type systems could then engage in more typical behavior with their own funds above and beyond what's made from deposits. Under such a regime no bank would ever be "too big to fail", customer deposits would be 100% guaranteed at all times, and more. In exchange you'd see substantially slower overall economic growth and monetary multiplication, but I'm increasingly convinced that would not have been a bad thing.
The Medicis couldn’t loan money at interest— that was usury—so they made money by charging a fee for allowing customers to deposit at one place and have the money available in other locations. That was not considered usury
I don't believe the claim that non-fractional reserve banking would actually slow economic growth.
Is real economic growth even determined by anything but technological development?
Of course, the economy can be made to "grow" by some slight of hand, like having a high inflation rate while pretending that we don't. Or by depleting natural resources. But that's not the kind of growth we want.
Some loans go to businesses so they can buy a new widget-making machine, employ more operators, and profitably sell widgets. Economic growth in action!
Other loans go to people who were going to buy a doodad after saving up for 12 months, who instead get the doodad immediately and pay for it for 14 months. That looks like economic growth, because in month 1 doodad sales have risen. But if the sale would have happened anyway, the 'growth' is lot more debatable IMHO.
So if no one got those loans, what would have happened to the resources they bought? What would've happened to the resources that went into building the widget making machine? What would have happened to the operator employees? Would they've disappeared? Most likely they would've become available to another investor who did not get the loan but also wanted to build a widget making machine.
Did the loan actually increase economic growth? I think the only reasonable answer is: Yes, if the bank issuing the loan had a better idea than the market about the future profitability of the investment. However, that doesn't seem very likely to me.
Of course this all is going to pale in comparison to the amount that banks make by d̶u̶m̶p̶i̶n̶g̶ ̶c̶o̶n̶s̶u̶m̶e̶r̶ ̶f̶u̶n̶d̶s̶,̶ ̶h̶e̶a̶v̶i̶l̶y̶ ̶l̶e̶v̶e̶r̶a̶g̶e̶d̶,̶ ̶i̶n̶t̶o̶ ̶h̶i̶g̶h̶ ̶r̶i̶s̶k̶ ̶a̶s̶s̶e̶t̶s̶ responsibly investing deposits. But of course banks under '100% deposits maintained' type systems could then engage in more typical behavior with their own funds above and beyond what's made from deposits. Under such a regime no bank would ever be "too big to fail", customer deposits would be 100% guaranteed at all times, and more. In exchange you'd see substantially slower overall economic growth and monetary multiplication, but I'm increasingly convinced that would not have been a bad thing.