The national currencies of various states can depreciate, which is called inflation. Inflation in a particular country always, as a rule, arises due to the inept management of economic and even political processes in the state by the government or intentional narrow-minded actions of a number of state officials. If fiat is used correctly, it only has a beneficial effect on the economy of the state. Therefore, it cannot be said that fiat is already outdated, it should be changed to other financial systems.
That sounds nice, if fiat was used correctly then a small amount of inflation every year will stimulate the economy, but that is not what happens in the real world, what happens is that governments find irresistible to abuse their power to print as much currency as they like and to spend as much money as they possibly can only to find out that there are consequences for their actions but when they realize that it is too late and they cannot fix it.