Blockchain has private and public chains.
Fiat is backed by what? It used to be Gold but Nixon removed it. Now the US dollar is under threat as it is the reserve currency backed by the petrodollar agreement that you can only buy oil with the dollar but that is now changing with the BRICS partnerships and Saudi Arabia is in talks with China about buying in Yuan.
Russia is saying it will only sell Gas in Rubles.
How do you get round this? A possibility is cbdc's of a dollar, pound, ruble etc. Then you use a crypto currency as a bridge asset like XRP or XLM to use a the exchange mechanism.