As far as I know, the ECB is not claiming that the digital Euro will be able to operate without electricity, instead they are saying that they can operate offline without a constant internet connection. Because to be able to use it, we also need electronic devices, applications...so it is absurd to say that it can work without electricity. Also, using Digital Euro without internet is just theoretical and we will have to wait until it officially goes live to know for sure.

Both CBDC and bitcoin are digital currencies, digital assets, so they cannot function without electricity. I heard that bitcoin can work without the internet, but I don't think it can.