pretty sure that ANY interventions by anyone would've been watched very closely by satellite and'd be all over you tube by now
Every civilian ship transmits its ID and position and can be monitored in real time (just like aircraft).
Not only can the location of every ship be seen, it can be recorded for later play-back - so it's easy to see which ships have been in an area.
For obvious reasons, military ships often do not broadcast their ID and location except when entering civilian ports.
They can of course be seen by
AWAC aircraft and satellites.
Approx route of nord stream 1 and the site of the rupture.
You can see how much marine traffic passes through that area. It would be impossible for any surface vessel to go un-noticed.
The logical conclusion is the sabotage wasn't carried out by a surface vessel, but something else.
GPS guided bombs from aircraft could certainly do the job, but easily tracked. Something below water line would seem the hardest to track.
What's more, anyone able to track a sub may choose not to admit they know who was in the area because it would give away their military capability.