The main thing is that when bitcoin completely replaces fiat, many intermediaries who change yuitcoin to fiat and vice versa will disappear. Fiat will simply disappear, with its endless emission and constant monitoring by banks and states. Unfortunately, such a pleasant future is still far away, even if several states have accepted the legalization of bitcoin. It seems to me that we have to wait for decades before this joyful moment.
I am a BTC supporter but I am really confused when predicting a future without fiat where everyone only uses BTC as the official means of payment through the Lightning Network. If this happens, people will learn to price everything in satoshi, and governments will no longer be able to print money to manage and operate the economy.
I think of another scenario: BTC will become a global reserve asset, or a peg for fiat. This means that fiat will still exist but will be limited by the BTC reserves of countries. At that time, maybe 1 BTC could have reached $1M or even higher.
As I think, FIAT will always be there in the future, crypto is just a support. We are fellow bitcoin supporters but there is nothing that makes us confident, that bitcoin will replace FIAT in the future.
Maybe we will see the popularity of crypto will be bigger and better in the future, but I don't think crypto will ever replace FIAT.
As long as there are traditional markets that still need Fiat, it will be difficult to replace it, but I agree that Bitcoin will only be a companion.
Even though bitcoin has been recognized and used as a legal means of payment, it will not be easy to replace fiat for all existing transactions.
Moreover, currently there are still many countries that are not fully willing to accept Bitcoin; it is only recognized as an investment or only for trading.
True, Bitcoin is becoming more well known but cannot completely replace the use of fiat.