When you receive the check, shouldn't you go to the bank and withdraw the cash with that? And bank lets you know that it is a fake check, thus denying the withdrawal. At what stage and why are you required to send your cash to someone else?
No, the bank doesn't know if it's a fake check straight away. They find out weeks later during a reconciliation process with the bank that printed the check.
To add more context: the check is usually not completely fake. It has a legit bank routing and account number on it, typically a business that is also being scammed. So the money will likely actually get withdrawn from some random business’s account and only discovered weeks or even months later.