https://www.federalreserve.gov/monetarypolicy/reservereq.htm

EDIT hmm that doesn’t link directly to the relevant FAQ:

“Why did the Federal Reserve reduce reserve requirement ratios to zero percent?

For many years, reserve requirements played a central role in the implementation of monetary policy by creating a stable demand for reserves. In January 2019, the FOMC announced its intention to implement monetary policy in an ample reserves regime. Reserve requirements do not play a significant role in this operating framework.

As announced (Off-site) on March 15, 2020, the Board reduced reserve requirement ratios to zero percent, effective March 26, 2020, in light of the shift to an ample reserves regime. This action eliminates the need for thousands of depository institutions to maintain balances in accounts at Reserve Banks to satisfy reserve requirements, thereby freeing up liquidity in the banking system to support lending to households and businesses.”