Most crypto (I believe currently approx. 90%) is mined outside of the US. Miners have already been moving from China to Iran[1], in part to avoid environmental regulations. As long as there exist jurisdictions that are not party to a carbon tax, crypto mining is highly incentivized to move there. Putting aside the issue of overreach, if the US wanted to reduce carbon, blocking inflows to crypto exchanges would be more impactful than taxing domestic mining.

[1] https://www.nasdaq.com/articles/inner-mongolia-to-shut-down-...