Earlier quoted context omitted.
It is in Russia's interest: this is their last warning before the North Sea pipelines blow up too.
Russia's greatest leverage was Europe needing their gas, and eventually agreeing to stop supporting Ukraine in order to get the gas turned back on. Now if the pipelines are destroyed, no matter how cold and angry citizens in the EU get, EU leadership has no reason to give in to Russian since that now won't get the gas turned back on. If anything, this points to Ukraine or the US doing it.
It can not possibly be in Russia's interest. They could easily nix NS2 at source. And now, even if diplomacy or desperation brings Russia to reach a peace deal with Ukraine, NS2 is out of commission for a long time. Does not compute.
US and UK certainly did not want NS2 and Biden did promise to "end it" if Russia invaded Ukraine. And the same day a Polish pipeline opens. But this is exceptionally risky if forensics turns up evidence that points to them. For one, it's an act of war against a fellow NATO member (Germany) and Russia; two, it sets a precedent that an island nation such as UK (with a lot of strategic pipes running in and out of it under Atlantic) can ill afford. So the risk factor seems to argue against that (though motive and who-benefits are clearly there).
Germany? It is possible that German deep state is not united. There are Atlantists and those who assert that German and Russian coexistence is optimal. The former faction could have done this to basically close that temptation/option to German government.
So that last group is imo the most likely culprit. [Honest question: if CIA acts covertly with say German special services (and not telling the guy in DC, you know, "need to know" and all that /g) and they do this, does that technically mean US committed an act of war or only CIA?]
p.s. whoever did this, it is a great advertisement for LNG delivered by ship escorted by blue water navies. This event just showed that gaspipelines are not and can not be strategically reliable energy conduits. They are trivially taken out of commission and repair (even if possible) will require great deal of time and resources to complete.