  The correlation between the mass of supermassive black holes (SMBHs;
$\mathcal{M}_{\rm BH}$) and their host galaxies ($\mathcal{M}_\star$) in the
reionization epoch provides valuable constraints on their early growth.
High-redshift quasars typically have a $\mathcal{M}_{\rm
BH}$/$\mathcal{M}_\star$ ratio significantly elevated in comparison to the
local value. However, the degree to which this apparent offset is driven by
observational biases is unclear for the most distant quasars. To address this
issue, we model the sample selection and measurement biases for a compilation
of 20 quasars at $z\sim6$ with host properties based on ALMA observations. We
find that the observed distribution of quasars in the $\mathcal{M}_{\rm BH} -
\mathcal{M}_\star$ plane can be reproduced by assuming that the underlying SMBH
population at $z\sim6$ follows the relationship in the local universe. However,
a positive or even a negative evolution in $\mathcal{M}_{\rm
BH}$/$\mathcal{M}_\star$ can also explain the data, depending on whether the
intrinsic scatter evolves and the strength of various systematic uncertainties.
To break these degeneracies, an improvement in the accuracy of mass
measurements and an expansion of the current sample to lower $\mathcal{M}_{\rm
BH}$ limits are needed. Furthermore, assuming a radiative efficiency of 0.1 and
quasar duty cycles estimated from the active SMBH fraction, significant
outliers in $\mathcal{M}_{\rm BH}$/$\mathcal{M}_\star$ tend to move toward the
local relation given their instantaneous BH growth rate and star formation
rate. This may provide evidence for a self-regulated SMBH-galaxy coevolution
scenario that is in place at $z\sim6$, with AGN feedback being a possible
driver.
