I think Ukraine isn't as backwards as people assume. And also has legal justification since they are at war with Russia. A crass motive is blowing up a pipeline that wasn't being used forces Russia to devote military resources to protect their oil and gas infrastructure elsewhere.

Western support of Ukraine is supposedly conditioned to defense of their own territory, not attacking Russian territory. This would be outside of that condition, so if they did it, it's best to keep it under.

It's more telling if they don't say, that would mean a Russian or Russian-allied operation is unlikely, because there is no political cost for shaming them even more.

NS was not on russian territory, it was sabotaged in international waters just a few km outside of danish territory

Still outside of Ukrainian territory, the condition for NATO support. And it only transports gas from Russia to Germany, with the winter approaching. Even more telling, the US statement in reaction to this was "a tremendous opportunity to once and for all remove the dependence on Russian energy".

I think western weapons come with those conditions for now. But Ukraine is free to attack targets inside/outside of Russia with their own stuff.

hmm, maybe someone should tell nato about the assassination attempt on alexander dugin inside russia, the suicide bomb attack on russian infrastructure, the helicopter raids into russian territory, etc

i don't think this attack is really as sophisticated as you seem to; the pipeline was about 80-100m underwater -- the ukrainians have (or had) oil platforms in the black sea which would require divers capable of operating at such depths. getting away with it is definitely impressive though.