85 out of 93 central banks (≈94% of global economic output) are engaged in some form of CBDC work, and while wholesale CBDC (inter-financial institution settlements) are likely to use Distributed Layer Technology (DLT) - it's not going to be a permissionless blockchain like Ethereum

Regarding retail CBDCs - i.e. the CBDC to be used by the broader public (used for ordinary transactions, essentially a digital version of the cash), those likely won't even use blockchain/DLT technology - at least for Advanced Economies