There are fundamental differences between fiat and bitcoin though.
Fiat is designed to lose its value over time. So, if you save in Fiat, then that's a pretty bad idea. You need to invest in any kind of asset with that fiat.
On the other hand, bitcoin is designed to increase in value over time, so you don't have to invest into something else. Although some countries consider bitcoin an asset, so that means ymthat you are saving in an investment instrument.
It makes a lot of sense to save in bitcoin, as long as you have a medium to long term in mind (5-10 years minimum )
In theory, bitcoin is designed to increase in value over time. But in reality, the value of an asset is determined by people's demand for it, and we cannot guarantee that the demand for bitcoin will always increase in the future. Therefore, although bitcoin is considered a good investment but it is still classified as a risky asset. And saving an asset that is considered risky is not necessarily a wise idea.
We often hear people advise each other to only invest the amount of money we can afford to lose in bitcoin, no one advises to put all of our savings into bitcoin. Right? Therefore, careful consideration should be given when using risky investment instruments like bitcoin as a savings account.