Russia is the only country who could do it without risking provoking a war.
Russia knew they weren’t going to make any money on it due to the strong reaction to the war on Ukraine.
Russia could have decided to do it to remind Western Europe that it could do the same to other pipelines they depend on.
None of that is determinative that Russia did do it, but it’s sufficient to me to indicate that they could have done it, and insisting that it’s absurd is, well, absurd.
Russia is also not a single actor. There are factions, and they have different interests. The "liberals" aka the economic bloc in the administration - who know full well what kind of shitshow is ahead in the long term - would prefer the war to die down, and for gas to start flowing again, preferably in exchange for dropping sanctions. Because of that, they're a potential threat to the war faction; think of how some parts of the German military repeatedly tried to arrange for secret negotiations with the Allies for an example of how it could materialize. But if there are no pipelines, the "liberals" have no gas to offer in exchange for concessions even if they somehow manage to stop the war and remove the war party from power. This makes their platform less attractive.
(To be clear, this is all just conjecture. The factions are real enough, and have motives that could make players in this game, but it's obviously not the only viable explanation.)
I find this the most likely scenario too. Blowing up the pipeline cemented that Europe wasn't going to get Russian gas for the winter. It left less maneuvering room to any interest groups that could've used it as a bargaining chip as Europe was heading into winter and many expected widespread heating and power issues, some local authorities in Europe even planned for possible mass evacuations of vulnerable population. Gas was the most valuable concession that anyone in Russia could've made. Pipeline blew up and that was off the table. Nobody knew at the time that winter 2022/2023 was going to be exceptionally warm and in hindsight it's easy to downplay those fears and percieved value of the pipeline.
You know the USA sends sophisticated military weapons and training to Ukraine including actual HIMARS used to blow up a Russian barrack and kill 400 Russians?
But you think the USA blowing up an inactive pipeline might be the thing that provokes a war and therefore the USA would never do it?
Russia knew they weren’t going to make any money on it due to the strong reaction to the war on Ukraine.
Russia could have decided to do it to remind Western Europe that it could do the same to other pipelines they depend on.
None of that is determinative that Russia did do it, but it’s sufficient to me to indicate that they could have done it, and insisting that it’s absurd is, well, absurd.