Your information is out of date. Alternative theories (such as modified gravity) have failed to explain the observations that separate dark matter effects from the distribution of matter.<quoted text>
From wiki - Dark matter is a type of matter hypothesized to account for a large part of the total mass in the universe. It's existence and properties are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe.
Do words like hypothesized and inferred make facts in your world? Dark matter is an inferential supposition based on speculation, and not all physicists agree with the idea.
Yes, its existence and distribution is inferred from gravitational effects on visible matter. We infer the location of things from effects on light all the time. The difference is minimal. The main question right now is not the existence of dark matter, but what it is made of.