  We report new results from the Neutrino Elastic Scattering Observation with
NaI (NEON) experiment in the search for light dark matter (LDM) using 2,636
kg$\cdot$days of NaI(Tl) exposure. The experiment employs an array of NaI(Tl)
crystals with a total mass of 16.7 kg, located 23.7 meters away from a 2.8 GW
thermal power nuclear reactor. We investigated LDM produced by the
$\textit{invisible decay}$ of dark photons generated by high-flux photons
during reactor operation. The energy spectra collected during reactor-on and
reactor-off periods were compared within the LDM signal region of $1-10$ keV.
No signal consistent with LDM interaction with electrons was observed, allowing
us to set 90% confidence level exclusion limits for the dark matter-electron
scattering cross-section ($\sigma_e$) across dark matter masses ranging from 1
keV/c$^2$ to 1 MeV/c$^2$. Our results set a 90% confidence level upper limit of
$\sigma_e = 3.17\times10^{-35}~\mathrm{cm^2}$ for a dark matter mass of 100
keV/c$^2$, marking the best laboratory result in this mass range. Additionally,
our search extends the coverage of LDM below 100 keV/c$^2$ first time.
