The old model ignored the inductor's parasitic elements. The new library includes proper CCM (Continuous Conduction Mode) and DCM (Discontinuous Conduction Mode) simulation. You will now see the sawtooth ripple on the output capacitor. Adjust your LC filter values in simulation and watch the ripple change in real-time—exactly like on a scope.
The updated library includes for these specific constraints. proteus lm2596 library updated