Fix for the white line problem on Steam Deck:

1. Enter Desktop Mode on Steam Deck, download dgVoodoo 2.78 (Jan 11, 2022) from dege-diosg's GitHub via web browser, and extract the zip file
2. In the extracted folder, double click the file dgVoodoo.conf to open in Kate editor
3. Go to Edit > Find, type "dgVoodooWatermark" without quotes, change the value from true to false, and then click Save to overwrite the file
4. Close the editor and return to the extracted folder. Copy the modified dgVoodoo.conf to the game directory .local/share/Steam/steamapps/common/Indiana Jones and the Emperors Tomb/GameData/bin (browse installed files via Steam to navigate there faster)
5. Return to the extracted folder. Copy the file D3D8.dll from [extracted folder]/MS/x86 to the game directory .local/share/Steam/steamapps/common/Indiana Jones and the Emperors Tomb/GameData/bin
6. Return to Gaming Mode, click on the game and go to Settings > Properties > General, and type WINEDLLOVERRIDES="d3d8=n" %command% exactly as is under "launch options"
7. Exit back to the main menu and launch the game

On Proton 8.0-5, I was able to enjoy the entire game from start to finish without white lines using this method and it ran flawlessly on Steam Deck OLED. Don't forget to bump up the resolution via in-game settings for the best experience. I have no idea if this works with mods or not. Later versions of dgVoodoo crash the game on start-up on my Deck. I shared my controller config "Indiana Jones and the Emperor's Steam Deck" under community layouts for convenience for anyone who wants to use it.