Actually I don't think that cryptocurrencies will replace fiat money in the nearest future. There are still too many people who don't believe in crypto and don't know how to use them. What is more, government can't control crypto and that's why they don't really want it to develop as this way they will lose control over people finances.
If you look at the development of crypto to date, it can be said that its development is very drastic,
although it is impossible for crypto to replace fiat in the near future,
besides that high fluctuations make it difficult to realize
Cryptocurrency cannot replace fiat. It was created to be an alternative to fiat, not to replace it. Therefore, it must coexist with the national currencies of states. In addition, for this to happen, an appropriate decision by the highest bodies of state power is necessary, as was the case in El Salvador. This is the only case so far, but even here bitcoin did not replace fiat, there was simply no national currency in El Salvador.