All money is made up. The banks literally "lend" money into existence without having it backed by anything, the banks don't need to have the money in the first place, the bank reserve requirement has been dropped to 0% in 2020.
Like I could give you 20 dollars and it’s made up in a sense, it’s just a piece of paper, but also you can go to the store and buy things with it.
Whereas if you’re an investor in a company and the CEO does some self dealing which nominally values your shares at 20 million, you can’t go spend that. It’s even more made up
"All money is made up, but some are more made up than others."
(in reality some of that $20B would probably make it back to bank A as money circulates, so the actual amount of reserve money that banks have to borrow depends on more complicated factors. This also doesn't talk about what happens if the borrower defaults. But the fundamental principle remains the same, and is what ultimately limits how much money a bank can lend).