The most likely suspect is still the Russians.
Their strategic goal has long been to split off Germany from the US/UK/EuroAllies block by basically paying off German politicians (see the slimy German Chancellor Gerhard Schroeder for example) using the river of money coming out of the ground in form of oil and gas.
But Germany successfully reoriented its energy usage and survived the winter. Putin knows know that pipeline will be useless for many, many years at least as long as he or someone like him is in power in Russia. Russian energy will be a captive supplier to China at bargain basement prices.
So blowing it up and blaming the US is exactly the kind of plan Putin and his secret police regime would fall back to as the next move to try to pry the Germans away and recreate the Molotov-Ribbentrop idea of dividing the territory of Eastern Europe between Russia and Germany.
The Eastern Europeans and even most Germans are no longer falling for it.
Possibly someone else did it. There is no way to evaluate Seymour Hersh’s narrative without knowing what US or foreign intel faction fed it to him and for what agenda.
I laugh when they talk about “investigative reporters” like Hersh “cultivating” sources in the intel community. It’s the other way around.
Did you eat paint chips when you were a kid?