Successful currencies meet three criteria:
(1) they are in widespread use as medium of exchange
(2) they serve as unit of account
(3) they are a stable store of value.
Most sovereign currencies fully meet all three criteria.
What about Bitcoin?
At the moment, some countries have taken bitcoin as a means of payment, and the number of stores and establishments where you can use bitcoin as a means of payment is increasing, but we need to agree with the fact that currently bitcoin is more used as an investment.