  The KM3NeT/ARCA neutrino detector is currently under construction at 3500 m
depth offshore Capo Passero, Sicily, in the Mediterranean Sea. The main science
objectives are the detection of high-energy cosmic neutrinos and the discovery
of their sources. Simulations were conducted for the full KM3NeT/ARCA detector,
instrumenting a volume of 1 km$^3$, to estimate the sensitivity and discovery
potential to point-like neutrino sources and an all-sky diffuse neutrino flux.
This paper covers the reconstruction of track- and shower-like signatures, as
well as the criteria employed for neutrino event selection. By leveraging both
the track and shower observation channels, the KM3NeT/ARCA detector
demonstrates the capability to detect the diffuse astrophysical neutrino flux
within half a year of operation, achieving a 5$\sigma$ statistical
significance. With an angular resolution below 0.1$^\circ$ for tracks and under
2$^\circ$ for showers, the sensitivity to point-like neutrino sources surpasses
existing observed limits across the entire sky.
