I don't think North Korea has the electrical capacity to mine cryptocurrencies. They don't have enough electricity to keep their cities lit at night.
My impression was that they aren't electrified because it isn't a national priority for them to be, not because they lacked the capable to develop the infrastructure.
It's in their interests to keep the people alive yet stagnant.
Serious question: If you're an elite NK party member with your own private home theatre set-up, who do you call when your Plex server stops working?
A lot of things need to line up to make the unit cost of mining bitcoin work.
They certainly don't devote enough capacity to do that, but that could be in part priorities for use.
And they have to ask themselves that question for every new kilowatt of generating power that they install.