The goal would be to create enough pressure from people - frustrated by problems like power cuts — so that governments must withdraw their support for Ukraine.
Any "WW III" fearmongering is similar : intimidate everyone into withdrawing support.
Many European countries have created emergency guides to help citizens preparing for crisis like this one. [2] This, I guess, has the underlying goal of maintaining trust in European governments.
[1] : https://www.politico.eu/article/russia-increasing-hybrid-att...
[2] : https://www.reuters.com/world/europe/eu-commission-urges-sto...
... Wait, how are you defining that? Much of the EU is about as close as it is possible to be to being at war with Russia without actually sending in troops.
so blackout is attack from russia. so stop spreading lies of terrorist russian state.
But Russia is an aggressive authoritarian state that was already caught for (smaller) acts of sabotage in EU, some of them quite dangerous. Why they are doing this? Who knows, war in Ukraine was not rational too. Perhaps some people want to be evil just for the sake of being evil.
As a Russian emigrant, I long stopped trying to rationalize Kremlin decisions. Why authoritarians are authoritarians? Who knows. Mad with power or something.
You cannot control stable governments, so you destabilise them with various tools for prolonged periods of time and then you end up with a country which is much easier to influence.
Same with the undersea cables.