On: Ethereum will use around 99.95% less energy post merge

[sudosysgen]

The only way to completely block access to the block chain thats remotely feasible are repeated 51% attacks and an impediment to general access.

That means raiding mining farms while limiting their number by limiting the size of Bitcoin.

Its only something the US or China could do.

Otherwise no, there is no way of completely blocking it. There are ways of making it impractical for the vast majority, though.