To be honest it’s a bit of a mine field at the moment but have a read of these posts (and sub posts if you have the time).
They are not specifically for the rift S but I used them with my CV1.
Do you have oculus beta installed?
Oculus debug tool is very useful too as you can set SS and reprojection from there.
I limited my frame rate in the rift CV1 to 30 using the CLI tool but I’m not sure of the syntax for the rift S.