The structures and properties of two-dimensional (2D) materials are profoundly governed by the interlayer coupling and stacking configuration. In particular, interlayer sliding can drive structural phase transitions and give rise to novel quantum phenomena in 2D materials. Here, we report a high-pressure study of structural and electronic properties in $\mathrm{N}{\mathrm{b}}_{0.6}\mathrm{R}{\mathrm{e}}_{0.4}\mathrm{S}{\mathrm{e}}_2$ up to 60.2 GPa. The synchrotron X-ray diffraction reveals a first-order isosymmetric structural transition from the $2H_c$ to the $2H_a$ phase near 16.4 GPa, driven by interlayer sliding. Concomitantly, a new Raman phonon mode ($M_1$) occurs at a critical pressure $P_c$ around 14.3 GPa and exhibits an anomalous redshift with increasing pressure, signaling substantial lattice softening. Superconductivity is observed at $P_c$, with a critical temperature $T_c$ of $\sim 4.4\mathrm{K}$. Strikingly, $T_c$ displays a notable nonmonotonic behavior, characterized by a prominent dome followed by a slow enhancement at higher pressures. We attribute the initial dome to the combined effects of phonon softening and a Lifshitz transition, while the reentrant enhancement of the superconducting phenomenon at higher pressures is closely associated with the evolution of carrier concentration, as evidenced by Hall effect measurements. Our results underscore interlayer sliding as a crucial mechanism for modulating electronic properties and suggest new avenues for realizing exotic superconducting states in 2D materials.

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• Phase transitions
• Pressure effects
• Superconductivity
• 2-dimensional systems
• Transition metal dichalcogenides