Walls need to be made specifically for Quest or PC and are not interchangeable between the two. You can tell which platform a wall is for by the file extension. .pixie files are for PC while Quest uses .zip files.
Inside the game in the main menu you will see on the left a CUSTOM WALLS button under the Mods section. Pressing it will open up the menu you can use to select which walls you want to use. There's also additional settings you can change, such as disabling the wall frames.