  We present the first comprehensive tests of light-lepton universality in the
angular distributions of semileptonic $B^0$-meson decays to charged spin-1
charmed mesons. We measure five angular-asymmetry observables as functions of
the decay recoil that are sensitive to lepton-universality-violating
contributions. We use events where one neutral $B$ is fully reconstructed in
$\Upsilon\left(4S\right)\to{}B \overline{B}$ decays in data corresponding to
$189~\mathrm{fb}^{-1}$ integrated luminosity from electron-positron collisions
collected with the Belle II detector. We find no significant deviation from the
standard model expectations.
