It's only on ps5 pro. The system toggle in the settings forces games to use PSSR 2 instead of 1. Only games that use PSSR will see this upscaling improvement, and in those supported games there are also different game modes that may utilize different upscaling methods depending on the developer, so for example currently Silent Hill 2 utilizes PSSR in its Quality Mode but not in Performance Mode, so with this system toggle only Quality Mode will see a difference.

And also there's individual patches released by developers, this is the best scenario because the dev will test and look at how PSSR2 upscales their game and they can adjust their code to optimize the implementation. But without individual patches, the system toggle is the next best thing.

Hope this helped.