All neutrinos are relativistic (moving at almost speed of light) and our current model assumes dark matter is "cold" (moving at relatively slow speeds).
A cooling gas of relativistic neutrinos becomes non-relativistic when the average neutrino momentum becomes comparable to their rest mass. The present cosmic neutrino background (CNB) temperature is about 1.9 kelvins corresponding to ~ 1.7e-04 eV/c^2 which is smaller than some neutrino masses.
This is still "hot" compared to Cold Dark Matter, and CNB also only a small fraction of the required CDM energy density.
The lightest cosmic neutrino background mass eigenstates could be relativistic at present, so how the CNB is split between (FLRW) radiation and dark matter is ripe for research. It will mostly be "hot" DM because of the heavier, colder species. But not hot enough to leave clusters of galaxies, unlike neutrinos produced by present-day astrophysics (and our own laboratory experiments and nuclear power generation).
https://en.wikipedia.org/wiki/Cosmic_neutrino_background
https://bigthink.com/starts-with-a-bang/cosmic-neutrino-back...
But I assume that in order for these sterile neutrinos to be dark matter they need to be really slow ...