You think that blowing up the Nord Stream pipelines would not be seen as an act of war?

No, because it happened in international waters ON THEIR assets.

It didn't happen in international waters. It happened in Danish, Swedish and Finnish waters. Denmark is in NATO.

And everyone in NATO is doing their best to ignore it, because they know where war leads.

People ignore acts of war all the time to keep the peace where nuclear arms are involved.

NS1 and NS2 aren't shipping any gas, and notionally are "Russian": dramatic but no change in the status quo.

Blowing a pipeline between two NATO members which is shipping gas and imperils their population is very different: NATO can't ignore that.

It happened in their "exclusive economic zones", not territorial waters. Very bad, but still leaves some place for manoeuvre.