DPRK has long been a source of high-quality counterfeit bills. I think this is just a sign of them trying to not to be left behind, as the world transitions away from paper currency.
Unfortunately, cryptocurrencies are resilient against counterfeiting, meaning they have to resort to tactics akin to that of a high-tech pickpocket or con artist. Since mining is highly energy-intensive and requires good connectivity, it would be a bad move for them.
Even without ICBMs and H-bombs, the only way anyone can do anything about North Korea is to make it more painful and costly for China to keep coddling them. Their conventional weapons deterrent is already quite effective. For decades, they've had the capability to flatten Seoul, without using a single nuke. That's already a price no one wants to pay.
So, besides sanctions (which only seem to make them mad), the only things you can do are to use cyberwarfare and go after China. Cyber is tricky, because by virtue of being so far behind the rest of the world, they have the tactical advantage of a very small attack surface. China is tricky because if you're not careful, they'll hurt you worse.