Fiat and cryptocurrency are the same but people in society differentiate them and value fiat because its adopted by the government far back, and since the existence of the world and also a specific country, so from my research I find out that government just disliked cryptocurrency for nothing,
So differentiating fiat from bitcoin is valueless because irrespective the importance and massive adoption of fiat currency from its existence before cryptocurrency, it's obvious that fiat is money and bitcoin is money, their functions and contribution in society never depart from each other, so bitcoin now is the shortest way of transactions across the world without much process or procedures, using bitcoin everything buyable is easier to purchase without stress, so from my perspective I prefer bitcoin than fiat currency due to fast transactions process across another country, and nothing fiat can purchase bitcoin can't purchase, so no difference between both because all are currency.
Even if we see them as performing the same function, they are not totally the same. During your daily transactions or maybe even in the past days, I believe you most have traded your Bitcoin or other crypto for any of the stable coins which by the way is pegged to Fiat currency like the USD? Bitcoin might have provided us the power to seamlessly transact across countries and continents faster but it's volatity is still an issue when it come to comparison with Fiat.