Not really forever. For a few thousand years, and a lot of the world found it completely uninteresting until Europeans got there. But it’s still fiat currency. All currency gains its value ENTIRELY from people’s willingness to accept it in exchange for good and services. Gold is NOT anything of value UNTIL there are other people willing to take it in exchange for goods and services, it IS fiat currency. ALL currency is fiat currency. Always has been, always will be.
The Europeans? Maybe you should go back an read some more history. The definition of fiat money is that it is made by A GOVERNMENT AND NOT BACKED BY ANYTHING OF VALUE NECESSARILY. you are correct that nothing is of value if it can’t be traded, but you can’t just make up your own definition of fiat.