My bank account is a digital store of value, in US dollars. I never visit the bank (was impossible during the lockdown), rarely handle cash, and when I do, it's inconvenient.
Your digital store of value promises to lose around 2% of its buying power every year, and they beat that by a lot this past year.
You can offset the inflation with your 0.5% savings account though... /s
Indeed, and I don't keep a lot of money for that reason. It's designed to be a relatively temporary store of value. There's no such thing as a guaranteed permanent store of value, because value is driven by markets.
Bitcoin is a guaranteed permanent store of value. It’s value comes from its scarcity, that isn’t going to change no matter what the markets do.
The value of a bitcoin will always be one bitcoin, just like the value of a dollar will always be one dollar. But you mentioned purchasing power, which can certainly change for both dollars and bitcoins. The "value" of a financial asset, of any practical importance, is its value relative to the value of other things.