Nordstream is also special because its destruction was not aligned with Russia interests. It limited Europe capacity to import Russian gaz lifting one of the reason which might have made the EU reluctent to fully support Ukraine (and causing a major economic crisis in Europe as a side effect).
Between this and the coyness of most European countries governments at the time to comment on investigation, it's not too far fetch to think that Ukraine might be involved.
Who did benefit most from the north stream sabotage? Not Russia, nor Ukraine, but the USA. Their gas replaced Russian gas imports.
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!
Wasn't the nordstream incident mostly elucidated ?
I believe they are only wondering about details now and trying to hear the guys.
https://www.wsj.com/world/europe/nord-stream-pipeline-explos...
https://www.intelligenceonline.com/government-intelligence/2...
https://www.france24.com/fr/europe/20240814-sabotage-de-nord...