  We present measurements of $B^{+}\rightarrow\rho^{+}\gamma$ and
$B^{0}\rightarrow\rho^{0}\gamma$ decays using a combined data sample of $772
\times 10^6$ $B\overline{B}$ pairs collected by the Belle experiment and
$387\times 10^6$ $B\overline{B}$ pairs collected by the Belle II experiment in
$e^{+}e^{-}$ collisions at the $\Upsilon (4S)$ resonance. After an optimized
selection, a simultaneous fit to the Belle and Belle II data sets yields
$114\pm 12$ $B^{+}\rightarrow\rho^{+}\gamma$ and $99\pm 12$
$B^{0}\rightarrow\rho^{0}\gamma$ decays. The measured branching fractions are
$(13.1^{+2.0 +1.3}_{-1.9 -1.2})\times 10^{-7}$ and $(7.5\pm
1.3^{+1.0}_{-0.8})\times 10^{-7}$ for $B^{+}\rightarrow\rho^{+}\gamma$ and
$B^{0}\rightarrow\rho^{0}\gamma$ decays, respectively, where the first
uncertainty is statistical and the second is systematic. We also measure the
isospin asymmetry $A_{\rm I}(B\rightarrow\rho\gamma)=(10.9^{+11.2 +7.8}_{-11.7
-7.3})\%$ and the direct CP asymmetry
$A_{CP}(B^{+}\rightarrow\rho^{+}\gamma)=(-8.2\pm 15.2^{+1.6}_{-1.2})\%$.
