There are no worries from the government about Bitcoin replacing fiat. There are those who don't have a problem with it. There are those that can accept it as legal tender, but we also know that there are still many countries that cannot accept it as legal tender and are only treated for investment and trade, but if you want to use it, it must be replaced with fiat.
But I'm not sure bitcoin will be able to replace fiat as a whole, because many people are still used to using fiat in several countries.
Perhaps because we are in the crypto market and follow crypto news every day, we have the feeling that crypto is really popular and widely accepted. However, the truth is that many people are still interested in other financial markets, other asset classes, and other areas such as science, politics, real estate...
BTC and crypto have taken a big step forward thanks to Spot ETFs and large-scale experiments, but they still need a lot of time to develop and assert their role in the economy, until they are accepted by investors as an important market similar to stocks and commodities. Until then, we can temporarily put aside the question of whether BTC can really replace fiat.