We appear to be using the term "in circulation" somewhat differently.
"Currency in circulation refers to the amount of cash–in the form of paper notes or coins–within a country that is physically used to conduct transactions between consumers and businesses"[0]
"As of February 10, 2021, there is approximately US$2.10 trillion in circulation, $2.05 trillion of which is in the Federal Reserve Notes (the remaining $50 billion is in the form of U.S. notes and coins)"[1]
...of course you're correct to note that this ~$2 trillion is only a proportion of total money supply (assuming we can agree on which measure to use for 'money supply') but it's still a substantial sum. It's also decentralized.
How does ~$2 trillion of decentralized money compare with the total supply of one's favourite (allegedly decentralized) cryptocurrency?
[0] https://www.investopedia.com/terms/c/currency-in-circulation...