Absolutely and literally not a bubble - your definition is in fact, not a bubble:
"It being a reserve currency means it can keep its value without having assets backing up that value, that is how we define a bubble".
FYI: Money has three functions: a store of value, medium of exchange and a unit of account. Fiat currency does not have assets backing it up for that you would need the gold standard that we abandoned in in the 70s.
A bubble:
"Bubble, in an economic context, generally refers to a situation where the price for something—an individual stock, a financial asset, or even an entire sector, market, or asset class—exceeds its fundamental value by a large margin."
And to your bitcoin comment: not even the slightest - bitcoin is not money it does not have the same functions it is a speculative asset investment (taxed on your gains, which money doesn't have).