Dyson sphere
en.wikipedia.org

... A Dyson sphere is a hypothetical megastructure that encompasses a star and captures a large percentage of its power output.[1][2][3] The concept is a thought experiment that attempts to imagine how a spacefaring civilization would meet its energy requirements once those requirements exceed what can be generated from the home planet's resources alone.

Because only a tiny fraction of a star's energy emissions reaches the surface of any orbiting planet, building structures encircling a star would enable a civilization to harvest far more energy. ...

So, as a side benefit, an advanced civilization effectively says to others trying to observe them ... look elsewhere?