No, but we have a theory that predicts several things, including something like dark matter. It has been tested for several of it’s large scale predictions involving the movement of matter. Now we are testing it’s prediction of physical dark matter.
We do know that dark matter, as constituted, in all its variations, requires observations grossly incompatible with what we, in fact, find.
Pop science cosmology presentations never, ever mention these contradictions. But it is, exactly, embracing contradictions like these that would make it science, not religion. Presentations without them actively mislead the public as to what science is and is for.
Trotting out details found (or made) consistent with DM amounts to indulging confirmation bias. An honest presentation describes the current favored theory, which summarizes a collection of observations, and then whatever is inconsistent with it. Sweeping inconsistent facts under the rug is the opposite of science.
Every substantial advance has come from embracing contradictions of current favored theories. Young people are inspired not by sweeping, broad-brush stories of how the universe is, but by mysteries that remind us how much is left to be discovered.
Biologists understand this. It is very easy to get a biologist to say "nobody knows". Every non-moribund field revels in what is still wholly unknown. Only cosmology circles the wagons against contradictory evidence.
I don't think i have ever heard anyone claim we know for sure. I have heard lots of physicists claim that its the best theory they are aware of given evidence they have seen, which is a really different claim.
> Biologists understand this. It is very easy to get a biologist to say "nobody knows"
We really like to tell stories where 2+2=4, etc.