Instructions to run ME3Tweaks Mod Manager semi successfully on the Steam Deck

instructions.md

The Steam Deck can run Mass Effect Legendary Edition with almost no fiddling (at least if you bought it through Steam; Origin installs will not be covered in this guide specifically but most of it should still work if you can get the vanilla game running), but modding it is a different story. You have to run a windows program that has graphical issues without config changes, and give it access to the game directory because the game runs in a sandbox. I will cover how to get the ME3Tweaks Mod Manager running well enough to install and update mods, and lay out the known issues and limitations.

As a reminder, the modding tool set is built for Windows. Linux is not supported and will not be supported in the forseeable future. Linux specific bugs will very likely not get worked on. This guide is to help the small proportion of users who want to use the mod manager on Linux despite the lack of support and the issues and difficulty it will bring.

Most of this guide will happen in Desktop mode, but by the end you can actually run the mod manager from within Game Mode. It is possible to do all this just on the Steam Deck, but a mouse and keyboard will make your life easier.

Prerequisites:

• Install and run each game at least once. If you can't get this far, this guide can't help you, and it won't let you install mods until you run it once anyway.
• Learn to use the mod manager. This guide will cover the specifics of running it on a Steam Deck, but not the general things that apply to the mod manager on windows.
• learn the very basics of the Steam Deck and the Desktop Mode.
• Install Bottles and FlatSeal from the Discover Store in Desktop mode. Bottles will let you make a configurable wine instance, and FlatSeal can give Bottles permission to access the game directory.
• Download The ME3Tweaks Mod Manager installer EXE and put it on your Steam Deck.

Setup instructions

1. Give Bottles Permission to access the SD card (might be optional if you are not running it from SD card). In Desktop mode, open FlatSeal, find Bottles in the list (or apply it globally), find the fileSystem section, and under Other Files, add "/run/media/mmcblk0p1" (without quotes) which is the SD card path.
2. In Desktop mode, run Bottles and make a new Bottle in Application mode using the plus sign in the upper left hand corner. The name doesn't matter, but make it specific to this. I call it M3, the common abbreviation for the mod manager.
3. Enter the bottle configuration by pressing any part of the entry besides the gears icon.
4. under the Preferences section, turn off DXVK. This should fix the huge UI issues some folks have encountered trying to do this.
5. Go back to Details and click the "run executable" button. Select the mod manager installer exe you downloaded earlier.
6. Install it somewhere. It doesn't really matter where, but remember the location, as we will need this soon. Note that the install path is within the Wine prefix of the bottle, so the path from outside will have mode on it.
7. After the installer runs, it will try to run the mod manager, but will just open an explorer window instead. This is fine. Double click the mod manager exe to run it. It should run mostly normally and you can do basic setup and install any updates. I recommend sticking with the light theme, as some things are very hard to read in the dark theme. Don't bother trying to set up game targets or mods yet.
8. Exit out of the mod manager. We are now going to make it easy to get back to this point. Note in the next few steps that this operating system is case sensitive.
9. Under the Programs tab, click the plus icon. You now need to navigate into the bottle's windows filesystem from the Linux filesystem. The bottles are, by default, stored at "/home/deck/.var/app/com.usebottles.bottles/data/bottles/bottles/". You may need to enable showing hidden files to navigate into .var, of you can type/copy/paste the full path. In that folder you should see a folder with the same name as your bottle. Go into that, then into the drive_c folder, and then navigate to the path you installed the mod manager at. So for me, using the default install location in documents, the full path is "/home/deck/.var/app/com.usebottles.bottles/data/bottles/bottles/M3/drive_c/users/deck/Documents/ME3TweaksModManager/ME3TweaksModManager.exe"
10. Double click to add it as a program.
11. Now test that you can repeatably launch it using the shortcut in the programs tab. You may need to change the working directory to match the directory it is in in the launch options.
12. If that works, I recommend clicking the 3 dot menu and clicking "add to library" (makes the shortcut accessible without navigating all the way into the bottle in the library tab) and/or the "Add to Steam" button which will add it as a non Steam game that you can launch from game mode. Note that launching it in game mode will have more visual glitches, especially with dialogs popping up, but you can do quick changes this way without going all the way to Desktop mode. I recommend the Web Browser controller template for this.
13. Now, we need to actually add the game as a target. Because the mod manager and the game itself are running in different wine based environments, it will not automatically find it. You need to point it at each game and the launcher. Open Mod Manager, click Add Target, and navigate to the game install directory, as mapped by bottles onto the wine file system. By default, it should have the SD card mapped to drive E, and the root filesystem mapped to Drive Z. You can customize this in the bottle preferences. If you installed the game on the Deck's internal storage, it will be at "/Home/.local/share/Steam/steamapps/common/Mass Effect Legendary Edition/Game" or similar. You may need to map a drive to get past the ".local" hidden folder. The root filesystem is mapped to drive Z. If you installed the game on an SD card, it will be at /run/media/mmcblk0p1/steamapps/common/Mass Effect Legendary Edition/Game" or similar. That will map to "E:/steamapps/common/Mass Effect Legendary Edition/Game" within the dialog to select a target. Add each game and the launcher.
14. Make a backup for each game you intend to mod before you mod it. No, seriously. Do it. This should not differ at all from the windows procedure, except for the weird file mapping. Place the backup on one of the mapped drives (Z or E), not within the C drive of the mod manager Wine container. It will make it much simpler to access if you need to, and the c drive has a default capacity that will cause you headaches.
15. I also recommend going into the mod manager settings under Actions > Options and setting the mod directory to a location on the SD card or Deck Filesystem rather than the c drive. This will help head off the same filesystem capacity issues mentioned above for large or numerous mods.
16. Finally, we can import and install some mods. Downloading directly into mod manager will not work currently. Directly download your mods within Linux or transfer the (still archived) mods from another machine. You can drag and drop mods onto the mod manager from the Linux file manager, Dolphin, and this will work seamlessly to import them into your library or install them. Other than the lack of ability to download directly in the mod manager from Nexus Mods, this works exactly like it would on Windows. Just like there, I recommend importing and then installing rather than installing directly. It will make your like easier if you ever need to redo things.
17. I have not tested the "Start Game" button in M3, but I would assume it will not work how you want it to. Launch the game via Steam, ideally in game mode to get controller/overlay stuff working correctly.

Enjoy your mods!

Confirmed working as expected:

• merge and DLC mods for LE1 and LE3. (LE2 should be no different, but I haven't tested)
• Install options UI
• Manage Target and restore from backup
• Drag and Drop mods onto mod manager from default Linux file browser
• Updating mod manager when it prompts you
• managing mods by launching the mod manager from within game mode (cannot drag and drop, will have graphical glitches)
• console within LE1 and LE3 (LE2 should be no different, but untested as of now)

known limitations/ issues:

(As these are Linux specific, and Linux is not supported, I would assume these will not get fixed. Do not bother the developers with these issues) can't download directly into mod manager from browser.

• "Start Game" button won't work how you expect it to.
• It thinks the ASI loader is not installed, and so will not let you install ASI mods in the UI. It clearly is installed because the console works and LE1 DLC mods work at all. I consider this low priority as ASI mods are almost exclusively developer focused. This issue might not be Linux specific, but have to do with non standard game install location.
• The mod manager can't launch to a browser. This means the easy Nexus authentication won't work and any prompts to download updates won't work. It will also break various links to help and documentation from within the app.
• Open in Explorer button will open a fairly useless explorer window within the M3 bottle

Untested:

(may get updated over time as folks test things)

• installing texture mods
• running LEX (why would you want to do this on this screen)
• other drag/drop operations like compiling merge mod, coalesced, etc
• advanced mod installation features such as squadmate merge, email merge, plotSync, TLK merge, etc.
• manually installed ASIs
• batch installer
• doing anything with LE2.
• running Trilogy Save Editor (I know it's not mod manager, but it's adjacent)
• mod specific configuration tools; ie EGM config, FemShep vs BroShep config

Other useful things:

save file location:

They do not make it easy to find you save files. If you want to access them to manually import saves/careers, they are at: "/home/deck/.local/share/Steam/steamapps/compatData/1328670/pfx/drive_c/users/steamuser/Documents/Bioware/Mass Effect Legendary Edition" I don't think the id will vary, but you can search for "bioware" within compatData to find the correct path if you are not sure. You will need to enable viewing hidden files or type it manually to get into the .local folder.

Really and truly get rid of the Origin Overlay

This should technically work with any game on the Deck that is installed via Steam but has its own copy of Origin. Within the same drive_c as above (or the prefix for any other game), search for igo64.dll. You should find two of them. rename them to anything else. I recommend igo64.dll.bak. Origin overlay is now dead for that game. This may need to be redone if Origin updates itself, and it must be done for each game within Steam individually, as they each have their own copy of Origin.

What do I do if the apply mod button is greyed out? It says "Cannot install to this game"

Some observations from following these instructions in the Year of our Lord Two Thousand and Twenty Five:

• The ME3Tweaks installer would run fine with the default "soda-9.0.1" runner, but the installed application wouldn't run. Creating the bottle with the "sys-wine-10.0" runner instead allowed ME3Tweaks to install and run correctly.
• Bottles needs, at minimum, permissions (via Flatseal) to read/write ~/.steam/steam/steamapps/common/Mass Effect Legendary Edition if MELE ain't installed to an SD card.
  • For drag-and-drop to work for installing mods, Bottles also needs to be able to at least read wherever you downloaded the mod files.
  • If you're gonna use Bottles for things other than ME3Tweaks you'll probably just want to flip the "All user files" switch in Flatseal, but obviously this ain't ideal if there are Windows programs that you don't want seeing your whole home folder
• The disk capacity limitations for backups were apparently inverted for me; ME3Tweaks would complain that I only had about 7GB of disk space when backing up to a Z: path (specifically, to MELE's steamapps folder), but the backups worked fine when backing up to a C: path (specifically, to ME3Tweaks' folder in Documents, alongside the existing mods folder).
  • The folder selection dialog doesn't offer an apparent way to create a new folder, as is necessary to create and select each game's backup folder, so I had to do that in a separate window (be it terminal or file manager).
• Whatever issue was preventing ASI loader detection seems to have been resolved; I can enable additional ASI mods just fine for all three games.
• Whatever issue was preventing opening browser windows has also been resolved; Nexus login works exactly as expected, as does opening mods' Nexus pages.
• Trilogy Save Editor's Windows version doesn't seem to run on Wine (UI doesn't actually render, though it does seem to respond to clicks, since clicking approximately where the "close" button would be closes the window). Worse, installing TSE seems to break ME3Tweaks with some .NET-related permissions issue. You're best off just running the Linux version natively.