MnPtGa hosts competing magnetic states, including ferromagnetic, canted antiferromagnetic, and spin density wave (SDW) order in the centrosymmetric P6₃/mmc structure, while a related inversion-broken structure supports chiral skyrmions. Controlling this competition motivates materials platforms that enable tunable strain and symmetry breaking, together with probes of SDW order compatible with ultrathin samples. Here, we demonstrate single crystalline MnPtGa membranes grown by molecular beam epitaxy on graphene/Ge(111) and released by mechanical exfoliation. X-ray and electron diffraction confirm high crystalline quality. SQUID magnetometry reveals a 140 K anomaly in the zero-field-cooled dM/dT that persists after exfoliation, while time-resolved reflectivity shows a coincident peak in the electronic relaxation time consistent with a quasiparticle phonon bottleneck associated with a putative SDW gap. Intentional rippling suppresses the ∼ 140 K magnetic anomaly, demonstrating mechanical control of the low-temperature state. These results establish MnPtGa membranes as a platform for detecting and strain-tuning competing magnetic orders.