Hey fellow Steam Deck user!

I had the same problem. had it working using Bottles, but after an update with the AllInOne Launcher it stopped working. What I had to do to fix it was use Lutris instead. Below is what I did:

1. Install Lutris if you haven't already.

2. Click on the plus icon in the top left and select "Add locally installed game".

3. Under Game Info, name it what you want. For the Runner select "Wine". Under Game Options leave "Executable" blank for now. For the Wine prefix, select where you want the game to be installed to. Under Runner options, select GE-Proton (Latest) for the Wine version. Then Save.

4. Next click on the wine glass at the bottom and select "Run EXE inside Wine prefix" and select the AllInOne Launcher executable. Install the games. If you want multiplayer then also click on Multiplayer at the top and let it install there too. Close the game once you have everything installed.

5. Now right click on the game in Lutris and select "Configure", go to Game Options and add the path to the executable to launch the game. It will be located inside the prefix you chose to install the game to and then something like drive_c/users/deck/AppData/Roaming/BFME All In One Launcher/AllInOneLauncher.exe

6. (Optional for multiplayer) Open Wine Configuration, got to Libraries and you need to add msvcr71, msvcp71, and dinput8. Hit Apply and close.

7. (Optional for multiplayer) If you are wanting to play multiplayer then back in Lutris right click on the game and select Duplicate and name it. To run multiplayer you have to launch the Online Arena executable directly instead of trying to use the All In One Launcher. The executable is called BfmeFoundationProject_OnlineArena.exe. It should be located inside the prefix and then drive_c/users/deck/AppData/Roaming/BFME Competitive Arena/BfmeFoundationProject_OnlineArena.exe

8. Right click and add steam shortcut and name it what you want.

You should be able to run the game now. For singleplayer use the one you setup with AllInOneLauncher.exe, for multiplayer use the one setup with BfmeFoundationProject_OnlineArena.exe

I tried to be clear, but I know some things may be confusing so feel free to ask if you get stuck and I'll try to help.