For every USDC in existence there is a dollar bill in a bank account somewhere. This is audited every month by Grant Thornton. $990,897,799 as of June 30th. USDC is fiat money riding on crypto rails.
So while USDC suffers from the monetary policy and capital control issues of The US Dollar, it's more user friendly. For example, try sending me $0.10 over the internet using your bank, or try wiring me $10k on a Saturday. Both are possible with USDC.