When you look into suspects we end up with more questions. Russia is an obvious one, they have ships in the area but why would they destroy their own important asset? They could use the supply of gas as a bargaining chip to lift sanctions in winter, perhaps they wanted to show the world they are still deadly scorpions on the world stage or they want to try and topple western civilization by destroying ocean infrastructure. They could cause everything to become more expensive. Plus they could tell their own population it is an attack on them and gain support for their war in Ukraine.
American submarines could have done it, but they wouldn't want to harm the economy of an important NATO member. Plus natural gas is already too expensive. But perhaps they were concerned that Europe would give in to Russia's pressure and lift their sanctions in winter so they took out Russia's last bargaining chip.
I thought it might be a privateer pirate. An organised crime syndicate that was paid by gas firms to blow up the gas lines so there is an artificial global shortage of gas so their own gas would become more expensive. Everyone would just blame Russia. Sounds like something out of a GTA game though.
Will we know the truth? Not sure.