From GT-Sport online manual.
③ Display Settings
The following settings can be adjusted:
・Exposure Adjustment: Adjust the exposure value (brightness) of the in-game visuals.
・Adjust Saturation: Adjust the saturation of in-game visuals.
・HDR Output: Set the HDR (high dynamic range) output on or off. This option is only available if you have a television that supports HDR.
・HDR Peak Brightness: Set the peak brightness (i.e. the brightest part of the screen) of your HDR (high dynamic range) television. This option is only available if you have a television that supports HDR.
・2K Output Mode for PlayStation®4 Pro console: Select the mode to use for PlayStation®4 Pro console 2K output.
"Prioritize Quality" offers high picture quality using the same amount of visual information as 4K output (4K downsampling), while "Prioritize Frame Rate" is a response-oriented mode (2K MSAA) that still offers higher picture quality than when playing on a PlayStation®4 console.
・Display Settings Assistant: Open the Display Settings that were performed during the first launch of the game. This will reset all settings configured so far.
Edit: It seems I've mistook Downsampling for Supersampling, and after some googling they are subtly different (still reading).
Edit again: Apparently they're the same thing, no idea