  We conduct a systematic search for protocluster candidates at $z \geq 6$ in
the COSMOS field using the recently released COSMOS2020 source catalog. We
select galaxies using a number of selection criteria to obtain a sample of
galaxies that have a high probability of being inside a given redshift bin. We
then apply overdensity analysis to the bins using two density estimators, a
Weighted Adaptive Kernel Estimator and a Weighted Voronoi Tessellation
Estimator. We have found 15 significant ($>4\sigma$) candidate galaxy
overdensities across the redshift range $6\le z\le7.7$. The majority of the
galaxies appear to be on the galaxy main sequence at their respective epochs.
We use multiple stellar-mass-to-halo-mass conversion methods to obtain a range
of dark matter halo mass estimates for the overdensities in the range of
$\sim10^{11-13}\,M_{\rm \odot}$, at the respective redshifts of the
overdensities. The number and the masses of the halos associated with our
protocluster candidates are consistent with what is expected from the area of a
COSMOS-like survey in a standard $\Lambda$CDM cosmology. Through comparison
with simulation, we expect that all the overdensities at $z\simeq6$ will evolve
into a Virgo-/Coma-like clusters at present (i.e., with masses $\sim
10^{14}-10^{15}\,M_{\rm \odot}$). Compared to other overdensities identified at
$z \geq 6$ via narrow-band selection techniques, the overdensities presented
appear to have $\sim10\times$ higher stellar masses and star-formation rates.
We compare the evolution in the total star-formation rate and stellar mass
content of the protocluster candidates across the redshift range $6\le z\le7.7$
and find agreement with the total average star-formation rate from simulations.
