  We present recent tests of lepton universality as crucial probes of the
Standard Model in semileptonic $B$-meson decays at Belle II. All presented
analyses use a data sample collected at the $\Upsilon(4S)$ resonance by the
Belle II experiment corresponding to an integrated luminosity of
$189\,\mathrm{fb}^{-1}$. We report three analyses that probe light-lepton
universality: The first measurement of a complete set of five angular
asymmetries using $\bar{B}^0 \to D^{*+} \ell^- \bar{\nu}_\ell$ decays, followed
by a measurement of the forward-backward asymmetry in untagged $\bar{B}^0 \to
D^{*+} \ell^- \bar{\nu}_\ell$ decays, and finally, measurements of the
branching-fraction ratios $R(D^{*+}_{e/\mu}) = \mathcal{B}(\bar{B}^0 \to D^{*+}
e^- \bar{\nu}_e) / \mathcal{B}(\bar{B}^0 \to D^{*+} \mu^- \bar{\nu}_\mu)$,
using the same untagged data set, along with the first measurement of the
inclusive light-lepton ratio $R(X_{e/\mu}) = \mathcal{B}(\bar{B} \to X e^-
\bar{\nu}_e) / \mathcal{B}(\bar{B} \to X \mu^- \bar{\nu}_\mu)$. Furthermore, we
present two tests of heavy-to-light lepton universality. In the first test, we
report the measurement of the branching-fraction ratio $R(D^{*}_{\tau/\ell})$
using hadronic tagging. In the second test, we present the first measurement of
the inclusive ratio $R(X_{\tau/\ell})$. All presented results are consistent
with their corresponding Standard Model predictions and, where applicable, with
the experimental world averages.
