Around the 9:45 min point in the video she suggests that the solution might be a change of behavior of matter, i.e. different phases of solid, liquid, gas, at different scales, from galaxies to clusters to the early universe. She says the ultimate solution to the dark matter problem might come from condensed matter physics instead of particle physics or general relativity.

I agree that this is a possibility.

"In the vast gulf between stars and galaxies, the temperature of gaseous matter routinely drops to 3 degrees K, or 454 degrees below zero Fahrenheit."

source: https://science.nasa.gov/science-news/science-at-nasa/2014/30jan_coldspot

Helium, a very abundant element in the universe, forms a liquid at these temperatures. Unlike a gas, which requires gravity to form clumps, liquids exhibit cohesion, and can form clumps even in the absence of gravity. Just as comets can form from clumps of various types of ice, helium might form liquid clumps in interstellar, and intergalactic space, if the temperature is low enough.

"At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temperature of −269 °C (−452.20 °F; 4.15 K)."

source: https://en.wikipedia.org/wiki/Liquid_helium

Below the Lambda point, Helium also exhibits the properties of a superfluid, becoming transparent, and frictionless.

"The Lambda point is the temperature at which normal fluid helium (helium I) makes the transition to superfluid helium II (approximately 2.17 K at 1 atmosphere)."

source: https://en.wikipedia.org/wiki/Lambda_point

So galaxies might be surrounded by a vast halo of super-cold, superfluid droplets, perhaps Helium (neglecting gas pressure effects), or perhaps some other as-yet unidentified element, or particle.

This phase of matter would not be manifested within a solar system because the temperature is too high near a star. In a solar system, standard Newtonian gravity would dominate. But in the cold interstellar and intergalactic spaces, transparent & frictionless superfluids might dominate. Being impossible to detect, except by the gravity they exert, it might seem as if there is some unseen mass, or dark matter, causing various mysterious phenomena: gravitational lensing, flattening of the angular velocity curves of galaxies, clumping of galaxies that should otherwise fly apart, etc.

IMO this idea has some potential.