The problem with Nordstream conspiracies was in fact that you could easily finger anyone as responsible, absolutely including Putin. The benefit to Putin (not "Russia" per se) is that it eliminated the revenue source from gas sales to Europe in the immediate term, and thus made "end the war now" less attractive to his domestic power base (because it wouldn't make them any more money for a few years).

A coup from disaffected underlings unhappy with the status of the Ukraine war is hardly a weird theory. He's fought off one already!

Pointing that Ukraine benefited most from the sabotage is not a conspiracy theory. It would be if there was another significantly more likely explanation but there isn’t.

Russian involvement is a bit far fetched to me. It severely limited their ability to export at a good price when gaz sell is how they finance the war in the first place, and removed their main pressure point on Europe therefore making the war considerably harder to win.

A third party would be more likely (there is a long list: could be the USA, a European country which wants the block to align strongly with the USA, or another power benefiting).