That sounds like a great idea for a sci-fi novel, but before I steal and write it I thought I'd ask ChatGPT if it already exists, and it seems it does.

"The Forge of God" by Greg Bear The Makers deploy a vast, self-replicating robotic spacecraft called the "Doomsday Rock" near Earth's sun. The purpose of this massive construct is to absorb energy from the sun, causing it to dim and ultimately leading to the freezing of Earth, thus rendering it uninhabitable.