The theoretical upper limit was around ~50 EV last time I paid attention, and I think they nailed it down somewhere around .28 eV, for scale an electron is about 2 million times more massive than that, and a proton or neutron around 4 billion times that. Neutrinos typically pop up in fusion level events paired to those guys, and the sun for instance spews out 2E38 every second, which sounds really impressive but is about a hundred kilograms a second. Now the entire galaxy emits pretty much in line with that, call it 2E49 of them, or 10e13, 10 Gigatons of neutrinos every second. Assume an effective 300,000 light years radius for us to care, these things moving at near light speed thus out of the galaxy, and you're looking at about 10E13 seconds or 10^26 kg of neutrinos in the general galactic region, roughly the mass of Neptune. That was raw napkin-math so it could be anywhere between Earth Mass and Jupiter, hell maybe even Sol itself, but pitifully tiny compared to the combined galactic mass even if we take those old theoretical upper bounds. Even if they didn't leave the galaxy as fast as they could, which they certainly do moving hundreds of times faster than the escape velocity of the galaxy and cheerfully able to slam through pretty much anything, the entire 10 billion year production time would only raise our figure to about 10E31, again the mass of the Sun. Pretty much no matter how you massage the data for upper bounds there's no way neutrinos can account for hidden mass in galaxies.