The surprising excess of missing-energy events far beyond all standard-model expectations in the weak decays of the charged ground-state B^+ meson into some charged strange meson, rather recently observed by the Belle-II experiment, may (easily) be explained by the decay of the B meson into the strange meson and a pair of dark-matter fermion and antifermion, mediated by an (intermediate) scalar or vector boson. Thorough inspections of both the total and the differential widths of these decays provide, among others, a simple means for the (straightforward) discrimination of such mediator boson's scalar or vector nature.
Berezhnoy et al. (Mon,) studied this question.