CBDCs have NOTHING to do with blockchain or cryptography or cryptocurrencies. They are digital in the sense that your credit card is digital which is to say that the liabilities exist in their base form on a digital (computer) medium, not physical(paper) medium.

You could choose to incorporate a blockchain in a CBDC implemnentation but why would you. Central banks have central in their name whereas a core value proposition of blockchain is decentralization. The Fed isn't going to wake up tomorrow and decide it wants to decentralize the dollar.