1. The US is already selling gas to Europe and there was no sign that would change. Europe has already committed to disinvesting from Russian energy. The pipelines were dead already. The US and others had already captured the market. Increasing the usage of Russian energy again during a bloody war against a neighbouring country would be political suicide for any European country I can think of. Maybe this is not obvious to Americans, and maybe this explains the obsessions with American intervention here - Americans always think their country is behind everything good or bad in the world, which in my mind explains a bit of the “Russia attacked due to NATO” delusional narrative. If anything happened in the world, US must be behind it, military industrial complex blah blah blah.
2. Like other posters here have already mentioned the consensus hunch (and that’s all we have - a hunch) for now is this was a warning to internal competitors in Russian internal politics. This was a way to burn the ships and end any idea that Russia will come back to the West. We are in unrestricted warfare against Russia. If you look into Russian propagandists online, they are 100% behind the idea that America did it to deindustrialise Europe, increase dependency, etc. I regularly follow the rule that whatever Russian propagandists say is higher in likelihood to be false, something which has been demonstrated again and again with - MH270 flight, invasion of Crimea, the killing of Boris Nemtsov, the Skripal poisoning, the invasion of Ukraine, now the usage of Iranian drones (Russia denies ever using them as they rain upon Kyiv).
3. Like others have said, there are other operational pipelines. Thinking the problem with Russia selling Europe energy is “pipelines” is the definition of missing the forest for the trees. Assume we are at war with Russia and that they are a full blown revisionist militarist state in the Nazi tradition and everything will make more sense. Stop making stuff up and start dealing with reality - we are in a state of direct economic and information warfare with Russia, and in a proxy hot conflict where we hope to annihilate their armed forces. They are acting accordingly.
Effectively the world is at war against a new form of fascist/hypernationalist superpower and you guys are arguing about who blew up a pipeline that the fascists would use to feed energy to their now sworn enemies.
Stop guessing. It was the fascists.
Purely statistically speaking (without considering any details), that's definitely what one should bet on [1] before other information is recieved. If someone didn't know any of the specific facts, it's obvious that their intuition is honed correctly if that's their default. That doesn't mean it was the US, but without further knowledge (which most people don't have because who has the time for that), it's a very good default setting considering actual world history.
1. https://github.com/binka/essays/blob/master/us_atrocities.md