I've been noticing these issues as well. Using the 1440p mode on PS5, there are noticeable slowdowns in areas with many other players, and even in some instances such as the outside areas of Rabanstre. Any time I look in the direction of the buildings in the distance the FPS drops.

The PS4 Pro settings in backward compatibility mode perform much better overall, without any noticeable change in visuals. The loading times are lower, and we lose the controller features, which is unfortunate.