This work examines the impact of Fe3O4—Water nanofluid, magnetic force, and double-diffusive convective properties on a steady-state, two-dimensional, laminar flow in an inclined square cavity containing four heated rectangular blocks. The temperature and concentration within the square blockage are greater than those of the left and right walls, whereas the other two walls are both adiabatic and impermeable. The study considers many parameters, including the volume percentages of cavity nanoparticles (φ = 0.0, 0.02, 0.04, 0.06), the inclination angle (γ = 00, 300, 600), the Hartmann number (Ha = 0, 50, 100), and the Richardson number (Ri = 0.1, 1.0, 10). An in-depth study is provided on the temperature, concentration, and streamline contours derived from the specified factors. Compared to changes in concentration and temperature, the results show that the flow fields are more significantly affected by the introduction of nanofluid. Both the flow and temperature patterns are significantly affected by the Hartmann number and the inclination angle. High Richardson numbers are associated with a drop in the average Nusselt and Sherwood numbers as the nanoparticle volume percentage increases, and vice versa. Nevertheless, the overall average Nusselt (Nuavg) and Sherwood (Shavg) numbers exhibit a decrease when subjected to a magnetic field, regardless of the Richardson number and inclination angle.