These KiCAD plate files were designed by user chchchchalex and merely adapted by Gondolindrim: silkscreen was adjusted, metal rings around the switch cutouts were added. These FR4 files add small "slits" that are meant to keep the gasket strips of the Valhalla case in place, as it is a common ocurrence with this keyboard (reported by many users) that the gasket strips eventually start being dislocated and fall down.
The original plate file from Noxary is the file valhalla_plate_outline.svg . I do not own the plate file, nor claim to. This plate file was publicly released by Noxary on their (now extinct) website to the users, a practice very usual in the keyboard hobby so keyboard owners can make plates for themlselves. This being said, I do not know under which terms Noxary released the plate files, because the file was simply released without any license or disclaimers whatsoever. Have this in mind when using them; I recommend using these files only for their intended purpose: making plates for the Valhalla keyboard.
The RELEASES page has a ZIP file containing gerbers that can be used to manufacture plates.