  This study aims at identifying luminous quasars at $z>5.7$ among
X-ray-selected sources in the eROSITA Final Equatorial-Depth Survey (eFEDS) in
order to place a lower limit on black hole accretion well into the epoch of
re-ionisation. We confirm the low significance detection with eROSITA of a
previously known, optically faint $z=6.56$ quasar from the Subaru High-z
Exploration of Low-luminosity Quasars (SHELLQs) survey. We obtained a pointed
follow-up observation of the source with the Chandra X-ray telescope in order
to confirm the eROSITA detection. Using new near-infrared spectroscopy, we
derived the physical properties of the super-massive black hole. Finally, we
used this detection to infer a lower limit on the black hole accretion density
rate at $z>6$. The Chandra observation confirms the eFEDS source as the most
distant blind X-ray detection to date. The derived X-ray luminosity is high
with respect to the rest-frame optical emission of the quasar. With a narrow
MgII line, low derived black hole mass, and high Eddington ratio, as well as
its steep photon index, the source shows properties that are similar to local
narrow-line Seyfert 1 galaxies, which are thought to be powered by young
super-massive black holes. In combination with a previous high-redshift quasar
detection in the field, we show that quasars with $L_{2-10 \, \mathrm{keV}}
>10^{45} \, \mathrm{erg \, s^{-1}}$ dominate accretion onto super-massive black
holes at $z\sim 6$.
