  We report on the reconstruction of various charmless $B$ decays from
electron-positron collisions at the energy corresponding to the $\Upsilon(4S)$
resonance collected with the Belle II detector at the SuperKEKB collider. We
use simulation to devise optimized event selections and apply them to the full
data set collected in 2019, corresponding to 8.7\,fb$^{-1}$ of integrated
luminosity. We fit the difference between half of the collision energy and the
$B$ candidate energy (in the $\Upsilon(4S)$ frame) for events restricted to a
signal-rich range in beam-energy-constrained mass to search for charmless
signals. Signal yields of approximately 80, 15, 20, 30, 90, and 160 decays are
reconstructed for the channels $B^0 \to K^+\pi^-$, $B^0 \to \pi^+\pi^-$, $B^+
\to K^0_S(\to \pi^+\pi^-)\pi^+$, $B^+ \to K^+\pi^0(\to \gamma\gamma)$, $B^+ \to
K^+K^-K^+$, and $B^+ \to K^+\pi^-\pi^+$, respectively. Yields and background
contaminations are compatible with those expected from simulation and
comparable with those obtained by the Belle experiment. The results show a good
understanding of the detector performance and offer a reliable basis to assess
projections for future reach.
