A Dyson sphere is a hypothetical megastructure that encompasses a star and captures a large percentage of its power output. 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.
Okay I did the same calculation but with Martian orbit as dyson sphere size, and 50% efficiency I got a wavelength of 3.4um so nicely in the infrared range of JWST.
I think the sphere would need to be like 99.95% efficient to be undetectable by JWST at Martian orbit radius.