Its possible that Russia would threaten cyber warfare particularly with Ukraine should the United States or their allies attack Russia physically. I'd say that the chances for this being a false flag would be greater though against the direct interests of the United States. If the US power grid goes down then you should ask yourself why didn't Russia play this card sooner? There has been reduced relations with Russia when Trump came into office because he had to posture that he was not a Russian agent. When in fact the greater threat to the world is the growing Chinese influence thereof. I'd say if the US power grid goes down then it would be by insider bad actors that want to bring the US to its knees for greater power and influence. If this occurs there will be greater internet censorship and more draconian policies and measures put into place that would make the measures from the COVID pandemic look like a walk in the park.
The thing is I can't see either of those nations
physically attacking the Russian homeland. What I am saying is that the
sanctions will provoke cyber attacks from Russia. I don't think any country in this scenario would be foolish enough to mount a ground assault on enemy soil. It almost feels like political suicide at this point.