In the case of the USA, I see that it is 0%.
Correct. You can see the Fed's press release here:
https://www.federalreserve.gov/monetarypolicy/reservereq.htm. The reserve requirements have remained at 0% to the present day.
What is it going to do? Lower the reserve ratio to negative and allow banks to lend even if no one deposits?
This already happens, and indeed, is how that majority of new money printing happens. Whenever someone approaches a bank to take out a loan, the bank creates a matching credit and debit at the same time. They give you $1000 of credit (for example), and simultaneously create a matching $1000 of debt in your name. The bottom line of their balance sheet doesn't change, but now you have $1000 you didn't have 2 minutes ago. This is brand new money with no additional reserve. The bank does not have to wait for someone to make a matching deposit before they can hand out a loan.