The mod is a ReShade preset for Red Dead Redemption. Its goal is to give the game a similar look and feel to Red Dead Redemption 2, while being very performance friendly.
Paste the file from the archive into the Red Dead Redemption directory (where PlayRDR.exe is located).
Launch RDR, press the Home key on your keyboard and select the installed preset from the list.
Then click on “Edit global preprocessor definitions”. The RESHADE_DEPTH_INPUt_IS_REVERSED variable will be set to 1, you need to change its value to 0.