this is a script that lets you install RF5Fix (higher resolution, the steam deck's 16:10 aspect ratio, better framerate, better draw distance, and all that good stuff) and a modified version of Kentun's controller fix with the DLC installer removed.
it's designed to be very easy to use. just run it, follow the prompts, and everything should be good!
the related steam guide is over here: https://steamcommunity.com/sharedfiles/filedetails/?id=3366398851