There's still the potential of a foreign cyber attack, or some kind of EMP disturbing the network, but the government will NEVER admit to it if it is the real cause. Best evidence for an attack would be if authorities keep saying they don't know the cause a few months after this.

They're not gonna admit that green energy left the energy grid unstable and caused this either. But if this is the cause of the blackout, you can expect the government to silently take measures to reinforce the grid, measures that are designed specifically to address this weakness. And there will likely be non-governmental providers and investigators that will be able to prove it over time.

So basically, I think people will need to be patient for the truth on this one, but also be careful not to forget about it, and allow their government to escape scrutiny.