Dark matter isn't just dark, it doesn't interact with normal matter. When galaxies collide when can verify via gravitational lensing that the normal matter smashes together while the dark matter continues unimpeded in straight lines through each other.

Stars also don't interact with other stars that way. AFAIK, the bullet cluster is not evidence for WIMPs.

you're correct, but it is very strong evidence for dark matter in general.

Yes, but the Dyson spheres the GP talks about are "dark matter in general". Evidence for WIMPs are elsewhere.

I think you got caught up by the misnaming of 'dark matter'. It's better to think of it as 'transparent matter'. It's non-interacting, not like a Dyson sphere which would obviously be interacting e.g. from it blocking what's behind it even if it itself makes no emissions.

So, aether?

A dyson sphere would block the light of stars sitting behind it on straight line of sight from us. That doesn't happen with dark matters. It's transparent. Unlike dyson sphere.

We're compelled to choose the option which requires the fewest assumptions. Dyson spheres involve a level of assumptions far beyond dark matter and dark energy. There would have to be Dyson spheres everywhere, that do not radiate heat, and that support some civilization that leaves very few traces.

Dyson spheres emit lots of light, just at lower temperatures than that of the star they encompass. You're basically running a Carnot engine with the heat reservoir at the temperature of the star, some number of thousand degrees, and the cold reservoir at a few degrees kelvin.

Clouds of gas and dust don't emit light, yet we know they exist and can estimate their mass. Couldn't we apply the same methods to Dyson spheres if this was the case?

Everything that has temperature emits electromagnetic radiation. Including clouds of dust.