at the end of every month and especially every quarter the bank submits its capital ratio and a bunch of other calculations to the regulators. if the ratio isn't good it has to increase capital reserves. if the ratio is good it can do share buybacks and dividends.
They can't loan out more than the deposits they have.
If you could open a bank, accept 10 dollars in deposits, and loan out 100, you'd do it! You'd loan it out to your best friend and keep the cycle going until you're rich AF.
You can't loan out more than you have, but even loaning out 10 of 10 dollars has some risk - if someone comes for their money and you can't get your money back from the people you loaned it to. And it definitely increases money in circulation since it's not parked there. But it's not a magic money printing machine.