  Additional spin-0 particles appear in many extensions of the standard model.
We search for long-lived spin-0 particles $S$ in $B$-meson decays mediated by a
$b\to s$ quark transition in $e^+e^-$ collisions at the $\Upsilon(4S)$
resonance at the Belle II experiment. Based on a sample corresponding to an
integrated luminosity of $189 \mathrm{\,fb}^{-1}$, we observe no evidence for
signal. We set model-independent upper limits on the product of branching
fractions $\mathrm{Br}(B^0\to K^*(892)^0(\to K^+\pi^-)S)\times \mathrm{Br}(S\to
x^+x^-)$ and $\mathrm{Br}(B^+\to K^+S)\times \mathrm{Br}(S\to x^+x^-)$, where
$x^+x^-$ indicates $e^+e^-, \mu^+\mu^-, \pi^+\pi^-$, or $K^+K^-$, as functions
of $S$ mass and lifetime at the level of $10^{-7}$.
