  Very recently, it was suggested that combining the Swampland program with the
smallness of the dark energy and confronting these ideas to experiment lead to
the prediction of the existence of a single extra-dimension (dubbed the dark
dimension) with characteristic length-scale in the micron range. We show that
the rate of Hawking radiation slows down for black holes perceiving the dark
dimension and discuss the impact of our findings in assessing the dark matter
fraction that could be composed of primordial black holes. We demonstrate that
for a species scale of ${\cal O}(10^{10}~{\rm GeV})$, an all-dark-matter
interpretation in terms of primordial black holes should be feasible for masses
in the range $10^{14} \leq M_{BH}/{\rm g}\leq 10^{21}$. This range is extended
compared to that in the 4D theory by 3 orders of magnitude in the low mass
region. We also show that PBHs with $M_{\rm BH} \sim 10^{12}~{\rm g}$ could
potentially explain the well-known Galactic 511 keV gamma-ray line if they make
up a tiny fraction of the total dark matter density.
