  We explain how Rashba spin-orbit coupling (SOC) in a two-dimensional electron
gas (2DEG), or in a conventional $s$-wave superconductor, can lead to a large
magnetoresistance even with one ferromagnet. However, such enhanced
magnetoresistance is not generic and can be nonmonotonic and change its sign
with Rashba SOC. For an in-plane rotation of magnetization, it is typically
negligibly small for a 2DEG and depends on the perfect transmission which
emerges from a spin-parity-time symmetry of the scattering states, while this
symmetry is generally absent from the Hamiltonian of the system. The key
difference from considering the normal-state magnetoresistance is the presence
of the spin-dependent Andreev reflection at superconducting interfaces. In the
fabricated junctions of quasi-2D van der Waals ferromagnets with conventional
$s$-wave superconductors (Fe$_{0.29}$TaS$_2$/NbN) we find another example of
enhanced magnetoresistance where the presence of Rashba SOC reduces the
effective interfacial strength and is responsible for an equal-spin Andreev
reflection. The observed nonmonotonic trend in the out-of-plane
magnetoresistance with the interfacial barrier is an evidence for the
proximity-induced equal-spin-triplet superconductivity.
