They are not up to date on any sources I trust downloading from.

I appreciate your input. A different, more suitable solution has been found.

How would I keep an offline installer updated? I don’t think you understand what the usecase is, here. I don’t legally own Stellaris on GOG. If I did, I’d just play the linux native version they provide.

That’s a huge piece of software to do this one thing…

You know this is a piracy forum, yeah? If I owned it, I’d just install the native linux version.

It was really that simple! Thank you so much, I had no idea proton could just be run like this.

Full tutorial for potential future readers:

First add the base game installer as a non-steam game and run it, then close the installer when it is done.

Go to the shortcut settings for the non-steam game (the installer) and set TARGET to "C:\GOG Games\Stellaris\stellaris.exe" and START IN to "C:\GOG Games\Stellaris"

Run the game to confirm it works. Close the game, then adjust and run the script. Start the game and confirm the DLC were added. It should just work.

I have also uploaded this script here https://drkt.eu/files/scripts/install-stellaris-gog-dlc-on-proton.sh

#!/bin/bash

# PROTON="$HOME/.steam/steam/steamapps/common/Proton 10/proton"
PROTON="/mnt/450G/SteamLibrary/steamapps/common/Proton 10.0/proton"
PREFIX="$HOME/.steam/steam/steamapps/compatdata/3543916168"

DLC_DIR="$HOME/Downloads/stellaris_4.2.3_(86961)_win_gog/DLC"

export STEAM_COMPAT_CLIENT_INSTALL_PATH="$HOME/.steam/steam"
export STEAM_COMPAT_DATA_PATH="$PREFIX"

INSTALLERS=$(find "$DLC_DIR" -maxdepth 1 -type f -iname "setup_stellaris*.exe")

if [ -z "$INSTALLERS" ]; then
    echo "No DLC installers found."
    exit 1
fi

echo "Running Stellaris DLC installers in silent mode under Proton..."
echo

for inst in $INSTALLERS; do
    echo "Installing: $(basename "$inst")"
    # /silent or /VERYSILENT
    "$PROTON" run "$inst" /silent
    echo
done

echo "Done. DLC should now be installed inside the Proton prefix."