Crypto and btc Don't need fiat for one reason :
Becouse to create crypto or btc you need electricity.
If the crypto or btc can be new currency it need something to back it.
And electricity is best becouse Everybody need electricity electricity is the most valueble thing in the world.
Fiat is based on debt so based on nothing just promese.
After electricity the good ones wich can back are
Salt and sugar.
But nothing cant beat the electricity.
You know bitcoin and other cryptocurrency needs electricity and internet connection/data to use it or to make transaction but it is not Backed by electricity. Also at this moment not all countries are accepting or allowing to use Bitcoin and the adoption of bitcoin is not yet enough to say that it doesn't need fiat. In my country even we are able to use digital currency freely, we still need to convert our digital currency like bitcoin into our fiat currency before we can use it to buy anytime, anywhere. Using Bitcoin and other digital currency as mode payments is still limited.