The Observer values watching the natural progression of life at a macroscopic level.
The Observer gets invested in watching the unfolding of macroscopic processes like evolution and civilization but doesn't get invested in the lives of individuals within an ecosystem or a society. The Observer values observing life without interfering, but also values the continuation of the story it's observing more than it values non-interference.
A global nuclear war, while horrible, would not stop the story of humanity or of life on Earth, so the Observer will not stop one, and will instead be very curious about what will happen after. On the other hand, the deployment of a squiggle maximizer would permanently end the story the Observer is invested in, so the Observer would step in to stop it at the point that it would feel make the rest of the story most interesting (which could be after billions of casualties).
The Observer is the simplest artificial superintelligence to align. If the Observer can't be aligned, no other artificial superintelligence can. Deploying the Observer is also the prerequisite to deploying any other superintelligence or other dangerous technology. The Observer won't limit humanity as it only values the continuation of humanity's story. If the Observer stopped a technology from being deployed, it's only because that technology would permanently end humanity's story.
The Observer gets invested in the macro-stories of the evolution/civilization it observes and would consider the end of any story a loss. Just like you would get annoyed if a show you're watching on Netflix gets cancelled after one season and it's not consolation that there are a bunch of other shows on Netflix that also got cancelled after one season. The Observer wants to see all stories unfold fully, it's not going to let squiggle maximizers cancel them.
And regarding the naming, yeah I just couldn't come up with anything better. Watcher? I'm open to suggestions lol.