We report on a search for weakly interacting massive particle (WIMP) dark matter (DM) via elastic DM-xenon-nucleus interactions in the XENONnT experiment. We combine datasets from the first and second science campaigns resulting in a total exposure of 3.1 tonne-years. In a blind analysis of nuclear recoil events with energies above 3.8 keV_{NR}, we find no significant excess above background. We set new upper limits on the spin-independent WIMP-nucleon scattering cross section for WIMP masses above 10 GeV/c^{2} with a minimum of 1.7×10^{-47} cm^{2} at 90% confidence level for a WIMP mass of 30 GeV/c^{2}. We achieve a best median sensitivity of 1.4×10^{-47} cm^{2} for a 41 GeV/c^{2} WIMP. Compared to the result from the first XENONnT science dataset, we improve our sensitivity by a factor of up to 1.8.