Russia. Saved you a click.
The best place to draw the line is Texas. More national identity than Texas and you're a nation-state, less and you're a state. The nationality of Texas is undefined in this scheme, which is just as they would have it.
P.S. people call extremely well-funded cybersecurity adversaries "nation-state adversaries" because those three words start with the letters NSA. It's a joke about US national security being the greatest threat to US private security.
When used in the politico-social sense that invokes national identity, nation-state still takes as a minimum requirement the functional sense of Westphalian sovereignty, which Texas lacks. Texas would probably be considered a nation-state in both senses if it was a nation-state in the functional sense; but as a subordinate unit of a Westphalian sovereignty it is not a nation-state in the functional sense, much less the narrower social sense.
Yes, it does, it distinguishes Westphalian sovereigns (like thr U.S.) from federated states (like Rhode Island).
This introduces the much more serious meta-problem of distinguishing commenters who merely happen to use 'Westphalian' from Lyndon LaRouche fans.
It is directly applicable, and not at all a used; the broader functional (Westphalian sovereign) and social (the functional definition + two-way close mapping to a nationality) definitions of “nation-state” are both technical definitions widely used (and distinguished by context) in the field from which the term originates. (Just like “consistency” has different meanings in a CAP context vs. an ACID one, except with less ambiguity for “nation-state”, because compared to the functional and social definitions of “nation-state”, the CAP and ACID definitions of “consistency” are far more likely to both be plausibly relevant in the same context.)
The common use in cybersecurity is exactly the functional definition, not an abuse of terminology.
Its a nation-state in the functional sense (a Westphalian sovereignty) but arguably not in the politico-social sense (a nation-state in the functional sense that is also aligned with a single national identity and vice versa), though like most Westphalian sovereigns where that is true, works very hard to align national identity with the state, and the former sense is mostly a clear, concrete distinction [0] while the latter sense is a platonic ideal which is, at best, approximated, so binary inclusion/exclusion is always something of an arbitrary line-drawing exercise.
[0] And mostly corresponds to status in international law, but there are exceptions
Microsoft is not making their own determination of who the state actor is and is just letting the three letter agencies' finger pointing fly with no evidence. There is however significant evidence indicating a country other than Russia in the FBI's Solarwinds report that contradicts the headlines if you read the body of the report.
Such as?
The narrative US = good, Russia = bad is true but only if you are in the US. In Russia you see the complete opposite.
Both US and Russian intelligence have lied in the past, it's part of their job.
For example, the intelligence agencies don't have the right to spy or attack their own population (as far as I know), but there is nothing that forbids them to ask an ally to do it and put the blame on someone else.
Russia denies doing it, and both US and Russia have interest into collecting this data, so starting from there, it's important to keep an open mind that the interactions between countries are not black & white.