About This File
EDIT: Nvidia updated Portal RTX to include their own presets. These likely aren't necessary anymore.
I made some custom presets for Portal RTX because it doesn't have anything lower than High. There's 3:
Low doubled my FPS compared to high while retaining good visual quality. The main drawback with Low is that reflections are disabled. Medium and Medium-Low are almost indistinguishable from the higher presets to me, so I'd stick with those if you want more performance while retaining great quality.
To use this, drag the file (rtx.conf) of the desire preset into the Portal RTX installation folder and overwrite the existing file. I have this set to DLSS off by default, but feel free to turn it on.