We do know know, there are so many people who would have loved to see Nord Stream blown up.

Our foreign minister for example in Poland, thanked USA for doing so :P I for example I'm happy NS2 got blown up, as it means relative safety for us. Germans won't be able to just go on about their business with Russia in the future.

There are two boats that are under primary suspicion. One Russian salvage ship named SS-750 that carries a mini-submarine, which circled around for no apparent reason in the vicinity of the explosion area 4 days before the explosion. Then there is another boat, a 50-foot (15.4m) sailing yacht named Andromeda, was reportedly near the site of two of the three explosions in the days before they occurred. Traces of military explosives were found on Andromeda.

The Andromeda ship was operated by an Ukrainian national, and rented by a company from Uzbekistan, the owner of which holds a Russian and a Ukrainian passport which resident is located in the annexed Crimea.

In addition there are around 5 more ships that have been in the area.

There have been and still are multiple investigations. Sweden and Denmark dropped the cases citing lack of jurisdiction/basis to continue investigation. Germany issued an arrest warrant toward suspected operators of the Andromeda ship.

There was an alleged leaked Dutch intelligence report that implicated Ukrainians that was given to the The Washington Post, but military analysts from Sweden and Denmark has expressed strong doubts of the practicality of an 15.4-metre sailing boat to do a 80 meter technical dive using a crew of 6 to plant that much explosives (over 500kg) and at 3 different sites. As such they has described the Andromeda theory as a distraction and false flag.

Or US/Norwegian forces covered by NATO exercises.

And what would be the reason in this theory?