Pretty obvious sabotage. Neither a whale, nor a trawl can do it. Who benefits is a different question.
Russia is economically damaged but once deciding that selling gas to Europe is not more an option, Putin has now a plausible excuse to not fulfill the gas contracts anymore, without being economically penalized for breaking those contracts, because... not my fault.
It is desperate also to spark the flames of war in their population. So can use also the issue as leverage to force apathetic Russian people that for some strange reason don't like to die to accept the new situation.
If Russian people keep refusing to fight in the war, the war is over. And if Russia lose this war, Putin is politically dead and will be removed from the power by any means necessary. And removed means, probably killed by its own people. He needs to put their citizens in a much worse situation, so can justify a full call to arms.
European Union does not have nothing to gain with this.
USA could benefit as gas seller and to force Putin to not use nuclear arms in Ukraine near the remaining pipes. Putin went to Belarus only few days ago.
Other could benefit for undisclosed reasons. (Edited the China could benefit part, it was clearly a stupid idea)