  We present a microscopic calculation of the phase diagram of the Ising
superconductor NbSe$_{2}$ in presence of both in-plane magnetic field and
Rashba spin-orbit coupling (SOC). Repulsive interactions lead to two distinct
instabilities, in singlet- and triplet- interaction channels. While we recover
the previously predicted nodal topological superconducting state in the absence
of Rashba SOC at large magnetic field with six pairs of nodes along
\(\Gamma\)-\(M\) lines, a finite Rashba SOC breaks the symmetry that protects
these nodes and therefore generally lifts them, resulting in a topologically
trivial phase. There is an exception when the field is applied along one of the
three $\Gamma$-$K$ lines, however. In that case, a single mirror symmetry
remains that can protect two pairs of nodes out of the original six, resulting
in a \emph{crystalline} topological superconducting phase. Depending on the
Cooper pairs' center-of-mass momentum, this superconducting state displays
either Bogolyubov Fermi surfaces or point nodes. Moreover, a chiral topological
superconducting phase with Chern number of 6 is realized in the regime of large
Rashba SOC and dominant triplet interactions, spontaneously breaking
time-reversal symmetry.
