I wouldn’t call this increase in money supply as a debt. There really is no one to pay interest to. Traditionally, a sharp increase in money usually means inflation, but if demand falls, that inflation might not happen.
If the low rates are causing money to move back into the stock market, this is not sign these companies are sound. The investors are just parking money out of T-bills.
If American banks are loaning to businesses who are severely affected by Covid-19, expect another banking crash. Even at near-zero rates.