Quantum spin Hall edge transport in 2D transition-metal dichalcogenides depends on whether their 1D edge channels are preserved under realistic substrates and device boundaries. Here we implement spin-orbit coupling in DFTB and GFN-xTB within the Amsterdam Modeling Suite, and apply it to (Formula presented.) (Formula presented.) heterostructures. Edge-projected spectra reveal robust edge states in (Formula presented.) ribbons; these states remain robust against a laterally infinite H substrate, which only shifts the Dirac point via long-wavelength corrugation without introducing additional in-gap states. By contrast, terminated H edges generate trivial dispersion branches in the same energy window that hybridize only weakly with the topological edge modes. In the bulk, Fermi-level states are (Formula presented.) -derived; at the small twist angle, lattice-relaxation-induced strain drives miniband reconstruction, whereas at the large twist angle, the layers become electronically decoupled. These findings suggest the conditions – controlled twist angle and avoidance of terminated H edges – for achieving quantized conductance and unambiguous spectroscopic detection of helical edges.