The question pertains to this entanglement between the nuclear and cyber domains, as it pertains to the development of new classes of both nuclear weapons, as well as the actors that are involved. This isn't a physics lesson, but one of the characteristics of nuclear weapons, particularly thermonuclear ones, is their ability to generate an electromagnetic pulse.
Electromagnetic pulse weapons are weapons that have been optimized for that, and have the characteristic of being able to affect any electrical system that is not adequately protected. What that means for countries and economies that are now increasingly dependent upon the digital economy and digital technologies is that deterrence is not just defined by the ability to deter an actor who can create mass damage in the physical domain. We can threaten hundreds of cities with nuclear weapons, but a single nuclear weapon generating an electromagnetic pulse can create mass effects that would bring chaos across a wide range of infrastructure.
That means that the threshold for countries to effectively join an elite club and be able to hold the world's digital economy to ransom has become much, much less. North Korea doesn't have to pursue the creation of thousands of nuclear weapons in order to threaten the world. It needs a few nuclear weapons that are able to create this kind of effect.
Second, and perhaps more importantly from the perspective of NATO-Russia relations, both the Russian Federation and the United States are now modernizing their nuclear capabilities. That includes replacing decades-old command and control systems that previously operated in a much more robust analogue way. There are concerns that this modernization means that we are going to be implementing technologies that are, first of all, much more susceptible to effects that can be generated through nuclear weapons designed to effect an electromagnetic pulse, and, secondly, that one of the ways of effecting deterrence may no longer be simply nuclear, but may be cyber itself. In other words, a cyber-attack against the command and control infrastructure may be a better way of being able to deal with it than necessarily doing a one-for-one missile cap.
This entanglement is something that is now starting to come to the fore. It certainly came to the fore in the case of North Korea, but I would also caution that with the modernization of nuclear arsenals on both sides, this entanglement will only grow.