I prefer the idea Putin wants to eliminate this future point of negotiation from underlings trying to oust him. Who will support someone to get rid of Putin now that they can't promise to reopen the valves and thus the profits to the oligarchs?

That’s absurd, like cutting your nose to spite your enemy’s face. Putin would have sabotaged the Polish pipeline instead of his own, after all it’s not as if Russian-Polish relations can sink any lower.

Yes, as absurd as let's say attacking the only country in the world that has a large percentage of population that actually supports you(many people in Eastern Ukraine speak Russian at home)?

He was expecting to waltz into Kyiv in a few days, decapitate the Ukrainian government (literally), not to have to wage an intense war of attrition. Of course he miscalculated because of piss-poor intelligence (the one thing the former USSR was usually good at), that doesn't make the original calculation irrational.

Now if he had sabotaged the Norway-Denmark-Poland Baltic Pipe, he would have achived the same objectives, preserved his own capital investment, and killed off a potential competitor to Russian gas. Sure, it would have been a direct attack against a NATO country, but so was the 2014 bombing of the Czech munition depot in Vrbětice.

Nordstream is at least 500 miles long and billions of dollars of Russian investment built to provide income long past the wars end. There's no abstract 'warning' worth destroying that investment. Just no.