The reason it "works" is that the farmers using this had long term, fixed electricity contracts.

So they can mine bitcoin using the cheap (relatively) pre-gas crisis prices.

But yeah, in practice it's a massive waste of energy and natural gas. Because the Netherlands generates about 60% of it's electricity from gas (and another 15% from coal), with renewables, nuclear and biomass making up the rest.

So what happens is that instead of using 1 unit of gas to provide 1 unit of heat, now you use 2 units of gas to provide 1 unit of electricity which gets turned into 1 unit of heat. This strategy is increasing fossil fuel consumption, and it only works because the cost of extra consumption falls upon the power provider, not the farmer.