Not even ultra power saving, but just the regular power saving mode is great too. I keep my S22 Ultra on that literally all the time, and it often lasts more than a full day of regular use, longer than my old phone. The baseline performance is so great that you never notice that it's been throttled.

The implicit assumption is that not only does a technologically advanced society exist, but they also have the ability and desire to create space-faring self-replicating robots. So, on top of the other restrictions involved with the Fermi paradox, you're adding: Being on a planet where the gravity isn't too strong for space launches using available materials. A society that wants to spread out into space and has the technological, economic, and political will to do so. And also having self-replicating robots that actually succeed at their mission.

This would be miraculously rare. Maybe something on the order of one in every few thousand galaxies has such a society. There's no guarantee that even we humans would be able to achieve that.