Why Russian? Because this is exactly the sort of thing they've engaged in in this conflict. In addition, nobody else have a remote reason to do this.
Ukrainian obviously if not Nuland ordered it, kill Europeans reliance on Russian gas and sell us LNG.
NSs are 50/50 JV so Russian would have to flood the repair bills if it resumes, that's a lot of zeros.
Except Ukraine does not at all benefit. Russia does, it is waging an active energy war on Europe. That Ukraine is behind is the propaganda line coming out of Kreml sources naturally.
Expense of repairing NS is several orders of magnitude lower than the cost of losing the war. Cost of repairing destroyed infrastructure in Ukraine was north of $350 billion a while ago, expect that bill to be passed on to Russia if "they" lose (whether that country will exist after the war is a different question as most minorities want to break it up).

2 Russian gas pipelines sabotaged by CIA?
-I thought a thread with such a whacky title would come from a nut job. I am not disappointed.
Why would USA sabotage gas pipelines that supply desperately needed energy resources to Europe when Europe is the closest ally to the USA? Biden is stupid but not that stupid. LOL Seriously the guy doesn't even think when creating clickbait now. It worked. I responded.
I am not a big Biden fan. But - Russia invaded and Nordstream 2 was completely halted. Immediately. As Biden said.Feb 7.
Nothing to see here..