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!

As some might know, the creators of plutonium have banned Steam Deck users from installing the plutonium launcher, there is a way around this, but you can't login to your account on Steam Deck.
This means that you CAN'T play plutonium online against other players, but because we can install Plutonium, we can install the LanLauncher and then use Bot warfare to play and level up against bots (it's a separate profile that isn't linked to you Plutonium or Steam account).
Now there are some limitations to the Steam Deck to install Plutonium and LanLauncher, mainly the fact that thanks to the anti-cheat on Plutonium prevents the Steam Deck to open the Keyboard to type anything we would need.
To get around it, we will need to prepare everything on a Windows desktop (PC/Laptop), I am NOT going to install a different operating system on my Steam Deck.
This install was done on a New Steam Deck that I got the same day OLED 1TB, and was updated to the latest firmware.

Note: Step 1-4 work for Call of Duty Black Ops 1, Call of Duty Black Ops 2 and Modern Warfare 3 and you will have bots installed at the same time.
For Call of Duty World at War you can use Step 1-4 to get Plutonium and LanLauncher ready.
For the Call of Duty World at War bot part: still figuring that out myself.

We are going to need 4 things to make this work:
Windows computer (PC/Laptop)
Steam Deck
E-mail that you can open in a browser
A browser installed on your Steam Deck (Google Chrome or Firefox work)

For the first step we need to install Plutonium, the LanLauncher and the bot warfare on a windows computer.
Follow one of the guides in ''Disclaimer and Notes!'' section of this guide, it will fully explain how to mod the games on windows, then come back to this guide.

Make sure it fully works, go in game and play a match to be sure that the bots actually spawn and level up once to see if the experience works
And don't forget to make the custom bot name if you want bots with custom names running around.

If you are wondering if the LanLauncher is properly working, you will see in the main menu, right top corner ''T6 plutonium'', the players online will always show 999 online and the server browser is empty, even when you fully disconnect from the internet.

Now that we are sure that the game works and we are happy with the bot names, we need to go to our desktop and make a folder, name it whatever you want to name it.
Now in this folder you need to put a copy off the LanLauncher folder from the guide, in this folder you should have:
Lan - ICO file
LanLauncher - Application
LanLauncher - Configuration setting
LLUpdater - Application

Now copy and paste the Plutonium.exe in the desktop folder as well
And go find your Plutonium install folder on your PC, should be installed in:
C:\Users\{Your User Name}\AppData\Local\Plutonium
And copy the whole folder and its contents, then paste it in the desktop folder like this.

Now right click on the folder and compress to ZIP file.
Then go to you E-mail that you can open in a browser (For example Gmail) and send this file to yourself, if using Gmail because it's bigger then 25MB it will put it on Google Drive.

Now onto the Steam Deck.
First we need to go to desktop mode.
Click on the Steam button and go to power option, then switch to Desktop mode.
From here we need to get to our browser and then go to our E-mail.
Download the folder we just made (Google Chrome Gmail worked best for me).
Then we need to unzip the folder and put the complete folder on the desktop.
now move the Plutonium.exe out the folder and place it on the desktop, we then have to open steam on the desktop and add Plutonium.exe as a non-Steam game.
Click at the bottom left ''+ Add a Game'', Add a non-steam game, Browse, Find the Plutonium.exe application and accept it, Add selected program.
Now we need to click on the COG symbol of the game and click compatibility, check force the use of a specific Steam play compatibility tool and I choose Proton 8.0-5.
Now launch it and let it install, it will download and install the folder as much as it can, however before it can finish it will throw up the login screen for Plutonium, we can't do anything with this, it won't allow us to open up the keyboard, no matter what we do, this is okay.
close out the login screen and the installer will probably still be running but frozen, go to the bottom right of the Steam Deck desktop and click on the Steam symbol, then exit steam to kill it.
Now reopen steam and go to Steam library on the Steam Deck desktop and click L2 (Left bottom trigger) on Plutonium.exe and click R2 (Right bottom trigger) on manage files.
It will open where the incomplete Plutonium is now installed, go into your custom made folder from Step 1 that you downloaded and open the Plutonium folder, move or Copy&Paste the contents:
bin - folder
games -folder
launcher - folder
storage - folder
config.json - JSON file
console - txt. document
info.json - JSON file

Into the incomplete Plutonium folder, overwrite all the files in here.
Close this folder.
Now go back to the custom folder and move the LanLauncher folder to the Steam Deck Desktop.
We now have to add the LanLauncher to Steam.
Click at the bottom left ''+ Add a Game'', Add a non-steam game, Browse, Find the LanLauncher application and accept it, Add selected program.
Now we need to click on the COG symbol of the game and click compatibility, check force the use of a specific Steam play compatibility tool and I choose Proton 8.0-5.
Start the program, it should bring up LanLaucher with the install paths that we had setup on our PC/Laptop windows desktop which are of course incorrect, this program also doesn't allow us to bring up the Keyboard and if we want to find the game by browsing, it would take forever and would make it to easy to mess something up.
So we need to go back to our PC/Laptop windows desktop to make it easier and faster.

Go to the LanLauncher folder on your Windows desktop one more time and Copy&Paste the LanLauncher - Configuration setting to your desktop.
Now open this copy and you would see something like this, it's a txt. file and the location of the game files will be depending on where you installed the games.
We now have to change the locations to where our game is installed on the Steam Deck.
To do so, go to Steam library on the Steam Deck desktop and click L2 (Left bottom trigger) on Call of Duty Black Ops 2 and click R2 (Right bottom trigger) on manage files.
Now type over on your desktop txt. file the game location.
Now do the same for the Plutonium.exe, click L2 (Left bottom trigger) on Plutonium.exe and click R2 (Right bottom trigger) on manage files.
The result will look like something like this (numbers are based on the app data and may be different for you).
Of course if you plan on doing the other games as well, then do the same for those (WAW, BO1, BO2 and MW3)
Then save the file and go to you E-mail and send this file to yourself.

On the Steam Deck, go once again to your E-mail and download the modified LanLauncher - Configuration setting.
Then head to your download folder and move or Copy&Paste the LanLauncher - Configuration setting to the LanLauncher folder and overwrite the setting in that folder.

Now we are all set to go and can head to our Game mode and launch the LanLauncher, it should display all your games and the proper game/plutonium launcher location.
Just click on if you want to play zombies or multiplayer and launch the game form there.

Go to desktop mode on the Steam Deck and into the discovery store, search for protontricks and download it.
Open it and select non-steam shortcut: lanlauncher.exe"
Choose to use the default wine prefix.
Then select the option for installing a windows component.
Then you will see a huge list of files, you need 3 files:
d3dx9
faudio
xact
Select them and click ok.
The app will close temporarily until it finishes downloading this file.
You will know that the file is done downloading if the app opens up again That's it (Might take a while, took me around 5 mins of waiting).
Now you should be able to hear the audio.

Now for the bots, if we play Black ops 2, we would need to press ` key to open the console, this button is normally not mapped on the controller, so we need to map it our-self.
Go to the LanLauncher application in steam and click on the controller icon next to the COG.
Then click ''Edit Layout'', go to a catogory that you would like to remap, I went for the Buttons>Menu Buttons>first option (2 cubes into each other) and then click X to remove, then remap it to the Keyboard button ` key (is under the ESC button)
Then in game, go to a game-mode you want, click on it and when in a lobby, click the remapped key, now to bring up the keyboard, press Steam + X and type xpartygo and enter, then hit B and the remapped key to get rid of the keyboard and console.
In-game click on pause and spawn bots.

For Black ops 1, you don't need to do anything to start a bot match, just launch combat training.

For Modern Warfare 3, you need to rebind 4 keys to represent WASD, I recommend rebinding the left track-pad.
To open the menu you can just press the up arrow, then use the now rebind WASD keys to move trough the menu and press A button on the right side to accept, Up arrow to close the menu again.

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! TWICE!

DON'T REMOVE:
Don't remove LanLaucher or Plutonium.exe form your Steam Library, this will also uninstall the entire folders that we created on the Steam Deck and we would have to do everything over again.

TESTING GAMES:
Call of Duty World at War - Campaign, Multiplayer and Zombies work (working on bots)
Call of Duty Black Ops 1 - Campaign, Multiplayer and Zombies work (have to switch gamepad on in-game setting)
Call of Duty Black Ops 2 - Multiplayer and Zombies works, Campaign doesn't work
Call of Duty Modern Warfare - Multiplayer works, Spec Ops and Campaign don't work

INSTALLING:
If you want multiple games at the same time, make sure to set them up all at the same time.
Like in the guides I said that when you start plutonium it will auto repair and update, making all the progress you made void, by deleting the necessary LanLaucher edits and Bot-warfare files.

My guides for Call of Duty Plutonium offline + bot progress:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3492250744
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3426986067
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3487680184
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3427236934

For Black Ops 1 only, you need to make a choice:
If you don't install the bot upgrade (Combat training), then you will have access to all the DLC.
If you do install the bot upgrade (Combat training), then you will have Prestige option and all the mp game modes available for Combat training, but no DLC will show up for MP and zombies.

The trick I used in my guides to make launching it easier/nicer, like play the LanLaucher, but make Steam count it as official Call of Duty, doesn't seem to work for me on Steam Deck, I don't know where it goes wrong.
But for playing your games, it's no issue, it will just not count the play time.

For now I'm stuck on this, I can't get it to work.
If you know how to, then leave it in the comments.
This is what I managed to get so far:
Run World at War normally once on the Steam Deck, not the LanLauncher.
Then close out of the game fully.
Now in desktop mode on your Steam Deck, you can go to file explorer and go to:
/home/deck/.steam/steam/steamapps/compatdata/10090/pfx/drive_c/users/steamuser/AppData/Local/Activision/CoDWaW/

This file location would be on windows where you install World at War mods.
You can make a ''mods'' folder on the Steam Deck here and put the bot_warfare mod in there, then when you start World at War with the LanLauncher, you can go to the mod tab and launch it (it shows in the list, but doesn't actually work), but it won't load it in the match.
I even tried using an older version of bot_warfare for World at War, but it had the same result.

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