  The discrepancies between data on rare $b$-hadron decays, controlled by the
underlying neutral-current transitions $b\to s\ell^+\ell^- (\ell = e, \mu)$,
and the corresponding Standard Model predictions constitute one of the most
intriguing hints for new physics. Leptoquarks are prime candidates to solve
these anomalies and, in particular, the scalar leptoquark, $S_3$, triplet under
$SU(2)_L$ with hypercharge $Y=-1/3$, provides a very good fit to data. Here,
for the first time, we entertain the possibility that the same scalar
leptoquark, responsible for the LFU anomalies, is the portal to a dark sector
consisting of two additional vector-like fermions, one of which is a candidate
for the cosmological dark matter. We study two scenarios, where the dark matter
candidate belongs to an $SU(2)_L$ singlet and triplet respectively, and discuss
the theory parameter space in the context of the dark matter candidate's relic
density and prospects for direct and indirect dark matter searches. Direct
detection rates are highly suppressed, and generically below the neutrino
floor. Current observations with, and future prospects for, high-energy
gamma-ray telescopes such as HESS and the Cherenkov Telescope Array are much
more promising, as they already provide powerful constraints on the models
under consideration, and will potentially probe the full parameter space in the
future.
