Given that central banks are among those slowest to adopt new and efficient technology (magnetic tape and paper documentation is still how most banks globally operate), and are guilty of the most inefficient and bloated structures and wasteful practices, I'd be very surprised if they were able to provide the most efficient energy usage were they to go into mining.
So aside from the political reasons why "CBM" won't be a cure -- they have to accept they're not even viable for consideration.
When you say efficient technology you're not talking about BTC right???
The average energy consumption for one single Bitcoin transaction in 2020 was 741 kilowatt-hours.
That's pure insanity to me... People need to stop turning a blind eye to what we are doing here, this isn't efficient, it's insane!