Just wanted to report back now that I've finished the game and say the game ran smoothly without any incidents on Steam Deck! I really did enjoy the game (Rinso the most) and playing on my Steam Deck helped make it a comfortable experience. Here's some tips if anyone wants to play on Steam Deck, it works without issue:
If anyone has questions I'm in the Empty Box discord too (@chocobreadroll)
*Note for Naming MC using Steam Deck (spoilering to be safe but it's just a command suggestion): since steam deck users can't change their "user" name in a sense, I suggest adding this to your Steam Launch command with your name before getting to far in the first playthrough:
WINEUSER=YourName USER=YourName USERNAME=YourName %command%
1. After downloading the Windows version of the game, extract it to My Files. Click inside the game folder, Right-Click on EmptyBox.exe, Select Add to Steam.
2. Either in Game Mode or Desktop Mode, open the Steam library, find the game, click on properties (gear icon), go to Compatibility, and select Proton Experimental. If this isn't selected the game won't run, I choose Experimental by default but you can try the other versions.
3. Any windows that may pop up during the game are treated as new pop up windows inside the game. You don't have to exit the game to get back to the game itself, you just need to press the STEAM button and scroll down the game menus options with the d-pad to find the game selection. It should be at the bottom titled "Empty Box". Clicking it, you can play as normal.
Meta Additions: In order to view meta content, you need to access your compdata where the game's information is being synced with wherever you've extracted the Empty Box game.
Example: /home/deck/.local/share/Steam/steamapps/compatdata/[GAME_ID]/pfx/drive_c/users/steamuser/Desktop/
*Note: If you can't find the game's compdata, make sure it's the most recent game you've played and sort the folders by Most Recent.
I have also seen people say they wanted to try to do multiple true end runs with their version of L. I haven't tested it yet but I copied, pasted, and compressed the extracted Empty Box folder by putting it on my main hard drive. If my theory is correct, without playing the whole game again, you simply need to:
1. Compress the game right before you start looping with Saken (aka before saves are disabled).
2. In a location different from where you extracted the original game folder, decompress it there. (Ex. For me, I had the game in my sd card, so I would decompress that version on my main hard drive)
3. Go in the folder just like you did when you first download and Right-Click on "EmptyBox.exe" and press Add to Steam again. This makes a fresh addition to your Steam library, I have tested it, it will duplicate the game in your unfavorited game list in your library. Just scroll down until you find the duplicate.
4. Again since this is just a theory, I'll need to check for myself. Use Proton Experimental again and start the game. The purpose is to make a separate compdata library of the game.
5. Run the game and see if the saves are different.
Theory Summary: If someone wants to check this lmk! When you add a duplicate game executable to Steam, the system assigns it a brand-new, unique 10-digit App ID and builds an entirely separate Proton Prefix (compatdata folder) for it. This process essentially creates an isolated virtual C: drive for each individual shortcut you add to your library. Because the visual novel writes its persistent choice tracking and save data directly into this sandboxed virtual environment, the duplicate instances cannot see or read each other's files. This should allow you to run separate playthroughs on the same Steam Deck.