There was a off hand comment in the Big Short book, about a Money Market fund, Reserve Primary Fund, that announced they couldn't pay back all debits, during the worst of the 2008 crisis. It was, "Money Markets weren't cash -- they paid interest, and thus bore risk, ..."

Its interesting to note that Money Markets pay out <1% interest now. When I searched for Money Markets to get the %, I got an Ad for "Donut" touting a 7% APY DeFi. They advertise they put money into StableCoins and earn a return. Customer Quote on the page, "I make so much money on interest, I can pay rent". My god, the collapse will be huge.