

RADV_PERFTEST=gpl gamemoderun %command%
Had to move the files containing "pak" from the base game directory/Main into RealRTCW/Main. The report below me has more detailed instructions. Other than that it worked like a dream!
It won't run unless you copy/paste the "pak" files in to the "Main" folder in RealRTCW. Please see the report prior to mine for more details.
This just takes moving files from one directory into another.
1: Install both RTCW and REALRTCW
2: Right click RTCW and select Manage -> Browse local files
5: Navigate to folder called Main
3: Select and copy all filess that have "pak" in the name. eg (sp_pak1.pk3)
4: Right click REALRTCW and select Manage -> Browse local files
5: Navigate to folder called Main
6: Paste all your "pak" files here
7: Run the game
On a note that affected my system personally. This game supports screen capture, my machine did not like this and would take a very long time to boot.
So I edited the cfg file in /SteamLibrary/steamapps/compatdata/1379630/pfx/drive_c/users/steamuser/Documents/RealRTCW/main
changing:
seta s_alCapture "1"
to
seta s_alCapture "0"
Running on Steam Deck - My Solution Install Return to Castle Wolfenstein (Steam original) Install RealRTCW Switch to desktop mode (if you aren't already) Open Both install folders via desktop steam using view local files (or find them if you know where you are looking) open the "Main" folder in each of the installs From the "Return to castle Wolfenstein>Main" copy all the "*.pk3" files over to the "RealRTCW>Main" (you can probably move to save space but I copied them in case of possible issues, if I decided to run original)
Close everything, return to gaming mode play as normal
Hope this helps anyone trying to run this

Doesn't seem able to find where the genuine game is installed on Linux
Game complained it could not find my RTCW install. Said that pak0.pk3 wasn't found, and to make sure it's in the correct location, except it doesn't specify where this is. The online FAQ for this mod says this is probably because I don't have a genuine copy of the game (I do, they are both installed via Steam). Could not find out where it was looking by running steam from console. So, I've hit a dead end I guess. I use Proton 7.0-2 from Steam

This version is broken, get the linux native version and build it from source following the instructions on the github page
Windowed is actually borderless windowed even if you set a resolution lower than your monitor size, there is no true windowed option
Even when the game "fixed" itself for a short period it still felt like there was some input delay
Fps drops to unplayble levels when moving the mouse, including on the main menu
Game would sometimes crash to desktop when breaking objects
Build the sourceport engine from this page https://github.com/wolfetplayer/RealRTCW Then get the moddb mod download https://www.moddb.com/mods/realrtcw-realism-mod/downloads/realrtcw-31 and put the .pk3 files from !copy the content of this folder into rtcw root directory/Main/ into the Main folder of your RealRTCW build along with all the .pk3 files from your vanilla RTCW install. Launch the game with RealRTCW.x86_64 and it'll be the same as the steam version except actually functional.
Sound effects missing are a deal-breaker to me
Some sound effects are reeally quiet or missing
Renderer2 doesnt work
Framerate nosedives as soon as you move your mouse.