That is a very abbreviated history. There are two pipelines, NS-1 and NS-2, both of which have two pipes each. NS-1 was operational until a turbine had to be repaired in Canada. The bureaucratic process to allow the repair was arduous, but finally it got done and chancellor Scholz did a photo-op in front of the repaired turbine.
Then the Russians played coy and came up with counter-bureaucratic reasons why the repaired turbine could not be installed. Presumably to put pressure on Germany, which was afraid of the 2022/2023 winter at the time.
Then two pipes of NS-1 and one pipe of NS-2 were blown up. Since no gas was flowing at the time, Russia had no reason to blow up its bargaining chip. Ukraine or the U.S. did have a reason.
Russia also delivered gas to Austria through a pipeline that goes through Ukraine and for which Ukraine collected transit fees until this year. Russia didn't shut down or blow up that pipeline.
From the point of view of the U.S. and Ukraine it does not make sense to blow up the Austrian pipeline because Austria is neutral anyway, so just let Ukraine collect the transit fees.
Germany of course must be pressured to be the second largest financial and weapons supporter for Ukraine, so hey, let's blow up the pipeline of our "ally".
Apart from Hersh's "the U.S. did it" theory, the Wall Street Journal recently blamed it on Zalushny. No other theories have emerged, but rest assured that if there were a credible Russia theory the Western press would shout it from the rooftops.
Putin has offered multiple times to either open the remaining pipe of NS-2 or to route gas via Turkey:
https://www.dw.com/en/putin-offers-europe-gas-through-nord-s...