I remember reading something somewhere that the gravitational lensing of dark matter (where light bends around and you can see behind) was evidence for dark matter being a thing that exists. Dark matter could really be anything though (ones I have heard about include WIMPs, primordial black holes, and supersymmetric particles like gravitinos), and we simply don’t have enough experimental data to know what it is. We know it exists as we see its gravitational effects in galaxies and such, but that’s about it.