I keep hearing this lately. Also, that GPU compute has been re-purposed from crypto to AI.
I had the impression that crypto was powered by ASICs for the last... many years. And that was why GPU mining (let alone CPU mining) was not profitable
GPUs used for mining don't translate well to AI at any large scale. It is all newly created (modern) hardware. Some miners who ran GPUs (and ASICs) have transitioned to running AI compute (CoreWeave, IREN, NScale, myself...), but that's not the same thing as taking the hardware and using it for AI. It is new hardware.
CPUs for mining crypto are a niche edgecase with very little liquidity and generally a bad idea, since it just incentivizes botnets.
Major cryptocurrencies are based on Proof of Work or Proof of Stake. There are other consensus algorithms.
https://en.wikipedia.org/wiki/Scrypt#Introduction
scrypt has been introduced to stave off ASIC and FPGA solutions.