“A nation doesn’t have any productive capacity”

Semantics. What a nation has is (a) businesses which produce, (b) earn money from what they product, which is then (c ) taxed to support the government. All that contributes to the the relative value of the currency as determined by FOREX trading.

I called it “productive capacity”. If you have another term for all that above, that’s fine.

This is no different between cryptocurrency and fiat money.

Indeed? What businesses produce, earn, and are then taxed to contribute to the relative value of a crypto?

or release a software that can hack bank accounts and everybody suddenly stops believing in USD

Counterfeiting is a problem for any store of wealth. If anyone ever figures out how to spoof the blockchain……look out below, as far as crypto values are concerned.