Singularity of harmonic measures for hyperbolic lattices

Let $\mathrm{\Gamma }<\mathrm{I}\mathrm{s}\mathrm{o}\mathrm{m}({\mathbb{H}}^n)$, $n\ge 2$, be a cocompact lattice containing a convex cocompact codimension-one subgroup in the sense of Sageev. We prove that every finitely supported admissible random walk on $\mathrm{\Gamma }$ has hitting measure singular with respect to Lebesgue measure on $\mathrm{\partial }{\mathbb{H}}^n$. The proof extends the method of Kosenko–Tiozzo, replacing Fourier analysis for a cyclic subgroup by a von Neumann dimension argument that also applies to nonabelian subgroups. As corollaries, we prove the singularity conjecture of Kaimanovich and Le Prince for cocompact hyperbolic lattices admitting a proper cocompact cubulation, cocompact Kleinian groups, and cocompact hyperbolic lattices with totally geodesic sublattices of codimension one. In particular, our result covers all cocompact hyperbolic reflection groups, cocompact arithmetic lattices of simplest type and cocompact nonarithmetic lattices arising from the hybrid and inbreeding constructions.