Measurements of electroweak penguin and lepton-flavor violating B decays to final states with missing energy at Belle and Belle II

The Belle and Belle II experiments have collected a 1.2 ab$^{-1}$ sample of collisions at a center-of-mass energy corresponding to the $Υ(4S)$ resonance. These datasets, with low particle multiplicity and constrained initial state kinematics, are an ideal environment to search for rare electroweak penguin $B$ decays and lepton-flavor-violating $B$ decays to final states with missing energy from neutrinos. Results from $b \to sν\barν$ processes and their interpretation are presented. In addition, we provide an overview of the search for the $B \to K^{*0}τ^+τ^-$ decays and the lepton-flavor violating decays $B^0 \to K^{(*)0}τ^\pm\ell^\mp$, where $\ell$ is an electron or a muon.