In this guide I'm going to explain how to mod Baldur's Gate 3 on the Steam Deck, by using a Mod Manager.

Note:
I'm not responsible for any issues with the Steam Deck, if you do any modding on the Steam Deck it will be your own responsibility! YOU HAVE BEEN WARNED!

I ONLY RECOMMEND DOING THIS IF YOU KNOW WHAT YOU ARE DOING, DON'T DELETE ANYTHING YOU DON'T KNOW!

Go to https://github.com/LaughingLeader/BG3ModManager/releases and scroll to ''Assets''.
Download BG3ModManager_Latest.zip.
When downloaded, you have to unzip it, best to unzip it to a new folder on your desktop.
Go into the folder and press L2 trigger on the mod manager and add to steam.
Now open steam on your desktop and go the mod manager, click on the cog symbol, properties and go to Compatibility, check force the use of a specific steam play compatibility tool and select Proton experimental.

Now launch the mod launcher, it will give you an error an wants you to install windowsdesktop-runtime-8.0.16-win-x64, which is a windows program and won't work out the box on steam deck.
So go to the bag symbol (left bottom of the desktop, 3rd symbol) in search bar type Protontricks, install the program, if you already have the program, then you can find it also in the installed section.
Launch it and find ''Non-steam shortcut: BG3Modmandager.exe.'' and press OK.
Select ''select the default wineprefix'', OK.
Install a windows DLL or component, OK.
Select ''MS .NET desktop Runtime 8.0 LTS and press OK.
Now let it install the program, It will re-open Protontricks when done.
You can now close out of Protontricks.

Re-open BG3ModManager, go to setting and preference.
If controls don't work, go to the steam desktop and click controller icon, change the stick to be a mouse joystick and the triggers to be mouse right click.
There are 3 lines that need to be filled in:
Game Data Path: Z:/home/deck/.local/share/Steam/steamapps/common/Baldurs Gate 3/Data
Game Executable Path: Z:/home/deck/.local/share/Steam/steamapps/common/Baldurs Gate 3/Bin
Override Appdata Path: Z:/home/deck/.local/share/Steam/steamapps/compatdata/1086940/pfx/drive_C/users/steamuser/AppData/Local/Larian Studio/Baldur's Gate3/

Now we just need to manually install the Script extender.
Go to: https://github.com/Norbyte/bg3se
Download the latest version and unzip it.
Move the DLL to: Z:/home/deck/.local/share/Steam/steamapps/common/Baldurs Gate 3/Bin
Easist way to open it, go to steam, go to baldur's gate 3, press L2 on the game and browse files.

Now for starting the game, go to Baldur's Gate 3, click on the cog symbol, properties And fill in the Launch option:
WINEDLLOVERRIDES= "DWrite.dll=n,b'' Proton_NO-ESYNC=1 %command% --skip-launcher

Now to install mods, go to the Nexus website:
https://www.nexusmods.com/games/baldursgate3/mods
Find yourself a mod you like and click on it, it will open the mod page and show you a description, some pictures.

When you find a mod you like, click on files, click on manual download and then slow download.
Then drag the mod from your download folder directly into the mod manager, make sure the mods land on the left side, if they land on the right, just drag them from right to left.
Now click on export and then save.
You can start the game like normal in steam.

To use the mods in-game, go to mod manager in game, go to installed tab and check-mark the mods you want to use.

Two IMPORTANT Note:
1- Make sure to see if a mod needs a requirement, on the description page it will tell you if and what is needed for the mod to work, it will then also give you the links to the mods.

2- The mod manager will tell you that the Script extender isn't installed properly every time you try to install a mod that uses it, this is a lie and you can ignore it.
As long as you install the script extender properly manually once, you can go into the main game and on the title screen in the bottom left it will tell you that the script extender is installed.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3498442654