  Symmetry breaking in topological matter has become in recent years a key
concept in condensed matter physics to unveil novel electronic states. In this
work, we predict that broken inversion symmetry and strong spin-orbit coupling
in trigonal PtBi$_2$ lead to a type-I Weyl semimetal band structure. Transport
measurements show an unusually robust low dimensional superconductivity in thin
exfoliated flakes up to 126 nm in thickness (with $T_c \sim 275-400$~mK), which
constitutes the first report and study of unambiguous superconductivity in a
type-I Weyl semimetal. Remarkably, a Berezinskii-Kosterlitz-Thouless transition
with $T_\text{BKT} \sim 310$~mK is revealed in up to 60 nm thick flakes, which
is nearly an order of magnitude thicker than the rare examples of
two-dimensional superconductors exhibiting such a transition. This makes
PtBi$_2$ an ideal platform to study low dimensional and unconventional
superconductivity in topological semimetals.
