how does Russia benefit of destroying those pipelines, though?
It benefits however US interests: Germany becomes a more stable partner, no matter how this thing turns out. Currently Russia is blamed, so the German reaction is more severe. In addition, LNG prices are higher, but I don't think that was the main reason for that operation in the first place. Blaming the US, even if their responsibility is certain, in a time of crisis won't happen as a united front against Russia is still needed.
The more I think about it, the more I come to the conclusion that Poland's interests didn't lead to such a operation. They have even more problems with high gas prices than Germany because they don't have long term contracts with Norway.