Abstract
Motivated by the recent twisted MoTe₂ experiment [arXiv:2601.18508], we develop a disordered interacting edge theory of a fractional topological insulator at ν_tot=4/3, consisting of two time-reversal-conjugated ν=2/3 fractional quantum Hall states. For an S_z-conserving edge, we uncover three distinct phases with two possible conductance values per edge in the long-edge limit: 2/3e²/h and 4/3e²/h. In the presence of S_z-changing perturbations (e.g., Rashba spin-orbit coupling), an interaction-induced insulating edge state can emerge without breaking time-reversal or charge-conservation symmetry, corresponding to the absence of a topologically protected edge state. We further provide an exact mapping to a noninteracting fermionic theory exhibiting Anderson localization. Our results showcase an explicit, experimentally relevant example that the edge-state two-terminal transport is insufficient to identify the ν_tot=4/3 fractional topological insulators.