Stellar Engineering projects would be obvious to us even now. A ringworld, dyson sphere or any matrioshka sphere would be obvious if the start itself is in detection range.
Sorry, I'm not even going to consider the Danikenite hypothesis without a shred of proof.
A race one million years ahead of us technologically would have already started reorganizing the galaxy / universe to better suit them. It would be staggeringly obvious if they started doing things like that.
I don’t agree that they would alter the universe to suit themselves simply because of how it would affect other sentient life.
Rather then alter this universe they might just rather create their own.
John