The 992 GT3 keeps the same 4-wheel steering as the 991 where this stepper motor takes the place of the toe link. overall we would say the suspension changes in the rear look to be focused on weight reduction. There wasn’t anything not good about the 991 rear suspension anyway.
The rear brakes have pretty trick ducting. This rear mini diffuser looks like the ones sold by Professional Awesome. They feed air into these scoops that direct air to the caliper and the center of the rear hat for cooling. GT3s have optional carbon-ceramic brakes and these brakes need a lot of airflow since they don’t have the thermal mass of iron.
The underbody has these NACA ducts that feed ducts cooling the CV joints. Believe it or not, these get pretty hot and a car that has a fully sealed up flatbottom can probably use some cooling airflow.