Yeah as I said, I don't believe much coming from these investigations unless all evidence is open sourced so that people can independently go through it and decide for themselves. But let's have some fun and play around with this theory. It could make sense for Ukraine to sabotage the pipelines for two reasons: 1. Less natural gas sales to Europe means less war capital for Russia (maybe a bit naive outcome?) and 2. to turn the EU even more against Russia (as long as Russia is blamed) which could increase the amount of war material gifted to Ukraine. That said, personally, I think this theory is too naive and simple. 

 -US intel mouthpiece NYT was quick to blame Ukr groups
-Would Rf would blow up their own pipeline, the effort of years of negotiations? This pipeline makes the bond between Germany and Rf stronger (this is a fear of the US), and as you say is a source of revenue for Rf. 
-Impact of oil prices on US elections, and Rf oil “sanctions” https://video.nostr.build/27ecaa79a503eee4148e0b841206d8b96e745050080e31e68d6253b89c827fcc.mp4
-remember 70% of the “gifted” funds and arms go missing. There is more graft than gift. Money goes to US, Ukr, and other oligarch class