I'm confident that the pipeline was attacked by eco-terrorists, here's why. First, something few people have discussed is the number of attack sites. A government actor, having high confidence that their bombs would detonate, would only hit one or two sites because fewer attack sites reduces the risk of detection. A less experienced actor, fearing that their attack might fail, would hit multiple sites because this increases their chances of success. Second, as many people have mentioned, Russia hitting their own pipeline (which they had already turned off) within enemy territory is unlikely. But referring to the number of attack sites again, if they did do it, they probably wouldn't hit multiple sites within enemy territory because that makes it far more likely they would be discovered. It's also never been their MO (in the cold war) to directly attack the west. Third, it probably wasn't a western government (as some have argued) because if they wanted to blame it on Russia, they would do it somewhere that only Russia can hit, not in locations that are within range of western civilians with scuba diving licenses. It just doesn't strengthen the case for blaming Russia to do it this way, if they were going to false flag they would hit an area that Russians can hit but that non-state actors would have difficulty in reaching.
It was Hunter Biden, in the pay of Burisma. They decided they had to finally get something for their money and Hunter had all these diving snorkels just laying around.