final.sh

#!/bin/bash

export CURDIR="$(cd $(dirname $0); pwd -P)"
export PROTON_VER=Proton-6.21-GE-2
export WINE="$CURDIR/$PROTON_VER/files/bin/wine"
export WINEPREFIX="$CURDIR/prefix"
export WINEARCH=win64
export PATH="$CURDIR/$PROTON_VER/files/bin:$PATH"
export XL_WINEONLINUX=true
export DXVK_FRAME_RATE=0
export __GL_SHADER_DISK_CACHE=1
export __GL_SHADER_DISK_CACHE_PATH=$WINEPREFIX
export DXVK_HUD=1
export MANGOHUD=1

cd "$CURDIR"

if [[ ! -d "$WINEPREFIX" ]]; then
    # Getting GE Proton 6.21
    curl -L https://github.com/GloriousEggroll/proton-ge-custom/releases/download/6.21-GE-2/Proton-6.21-GE-2.tar.gz | tar xz
    # Installing stuff with winetricks
    winetricks -q dotnet48
    winetricks -q vcrun2019
    # DXVK
    cat <<EOF | base64 -d > dxvk.patch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EOF
    curl -L https://github.com/doitsujin/dxvk/releases/download/v1.10/dxvk-1.10.tar.gz | tar xz
    patch dxvk-1.10/setup_dxvk.sh dxvk.patch
    cd dxvk-1.10
    ./setup_dxvk.sh install
    cd ..
    # FakeSteam
    rsync -ahvP $HOME/.local/share/Steam/steamapps/compatdata/0/pfx/drive_c/Program\ Files\ \(x86\)/Steam "$WINEPREFIX"/drive_c/Program\ Files\ \(x86\)/
    # Cutscenes
    mkdir -p "$WINEPREFIX"/drive_c/users/steamuser/Documents/My\ Games/FINAL\ FANTASY\ XIV\ -\ A\ Realm\ Reborn/
    
    echo -e "<FINAL FANTASY XIV Config File>\n\n<Cutscene Settings>\nCutsceneMovieOpening 1" > "$WINEPREFIX"/drive_c/users/steamuser/Documents/My\ Games/FINAL\ FANTASY\ XIV\ -\ A\ Realm\ Reborn/FFXIV.cfg
    echo -e "<FINAL FANTASY XIV Boot Config File>\n\n<Version>\nBrowser 1\nStartupCompleted	1" > "$WINEPREFIX"/drive_c/users/steamuser/Documents/My\ Games/FINAL\ FANTASY\ XIV\ -\ A\ Realm\ Reborn/FFXIV_BOOT.cfg
    # XIVLauncher
    curl -LO https://kamori.goats.dev/Proxy/Update/Release/Setup.exe
    "$WINE" Setup.exe
else
    "$WINE" "$WINEPREFIX"/drive_c/users/steamuser/AppData/Local/XIVLauncher/XIVLauncher.exe
fi

On line 47, you should probably use steam's FFXIV app ID of 39210 and associated checks to see if that directory exists or advise installing FFXIV via steam and rerun the script.