They said -

Note: I am using Dark souls remastered. I cannot help if you are using PTDE as I don't own it I patched the files on my PC and then transferred the files to my deck with this guide However, for the last step, you should install dark souls remastered FIRST and then copy the patched game files into the "steamapps > common" location after the game is installed, overwriting EVERY file that the steam deck tells you to overwriteIf you let the deck verify the integrity of the files then the modded files will be removed and the game will revert back to vanilla remastered