Firstly what is the word store of value;store of value is something that maintain its worth both in the present and the future.Money is a type of assets in an economy that you can use to buy goods and services from other people or businesses.One of the functions of money in an economy is that it's serves as a store of value.
A store of value is something people use to transfer purchasing power from the present to the future.
While money is an asset that can store value, and also Gold and silver for example, acts as store of value.
Since money is accepted as a store of value, trade is much more efficient.When an individual or business accepts money in exchange for a goods and services, the seller can store the money in a bank account and retrieve it later in the future.
And as you can probably infer from your own explanation fiat currencies are not a store of value, in fact they do the opposite as instead they steal from anyone that decides to use them to save their wealth over the long term, and this explains why the rich are always buying everything they can with their fiat money, as they know that if they were to keep their wealth in this way they will lose more and more wealth, and this is simply unacceptable for them.