Fiat is a Digital currency without Value
Everything has a value. Some things have so low value that is close to zero. Value gets set on the market by supply and demand. Things with low value have big supply and low demand for it. Things with high value have low supply and demand for it.
That's right, even a certain trash can have a value once you recycle them or sell it to the junk shop. Don't underestimate things if it has a value or not, there are things in the world that you think it don't have any value at first but it have. Just like fiat, many people are using this in many transactions, many people are engaging in using fiat and also with cryptocurrency because they know that both of it have value in the market.
Fiat have value as anything else.
If you think that fiat don't have value, then don't use paper money, don't use physical money in your transaction and use it as a mode of payment. If you don't believe on fiat, then stop using also cryptocurrency because other cryptocurrency only depends on the price in terms of fiat. Fiat is one of the most essential currency before bitcoin, there are things that the fiat can do and not the bitcoin.