The government borrowed money in markets, which it has to pay back. We bought those bonds as a way.... Because our policy rate was at its effective lower bound, we couldn't lower our policy rate any more. A different way to lower interest rates is to buy government bonds, which pushes their price up and drops their interest rate. It's a different way to lower interest rates. It's not monetizing the debt. That did provide stimulus.
On March 3rd, 2022. See this statement in context.