Fiat currency and cryptocurrency are not the same. Fiat money is a government issued currency used as a legal tender, backed by a government. Examples of fiat currency are US Dollar, Euro, GBP, Yen etc.
Cryptocurrencies like Bitcoin, Ethereum, Cardano, Dogecoin are not backed by a government or central bank. They are based on a decentralized structure consisting of a network, that is distributed across a large number of computers in many countries.