As I said, the motivation isn't particularly compelling. But it should be noted that were Russia to have done it, it wouldn't have lost very much (the pipelines were no longer in operation at the time of the explosion, with NS2 never coming online, and NS1 having been shut off "indefinitely" a few weeks prior) and risked relatively little blowback, as Russia had already lost all credibility in the West when it invaded Ukraine. The gains aren't much, though. Primarily, it would have been a punitive action ("You want to support Ukraine? Okay then, freeze to death come winter!"), although it was noted at the time that the explosions weren't that far from a new Norway-Poland gas pipeline that had just come into service--a demonstration of capability. Unclear attribution could also be used as a lever to try to weaken NATO, by sending the US and EU into mutual recrimination.
All said, it looks like a low-risk, low-reward situation for Russia, which isn't exactly compelling evidence.