  Ultralight dark matter interacting with sterile neutrinos would modify the
evolution and properties of the cosmic neutrino background through
active-sterile neutrino mixing. We investigate how such an interaction would
induce a redshift dependence in neutrino masses. We highlight that cosmological
constraints on the sum of neutrino masses would require reinterpretation due to
the effective mass generated by neutrino-dark matter interactions. Furthermore,
we present an example where such interactions can alter the mass ordering of
neutrinos in the early Universe, compared to what we expect today. We also
address the expected changes in the event rates in a PTOLEMY-like experiment,
which aims to detect the cosmic neutrino background via neutrino capture, and
discuss projected constraints.
