Props to this guy for giving an idea:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3439588144

Originally posted by noirekld:

Disabling split screen with AHK (Auto Hot Key) for dual monitors

I have 1920x1080 (Full HD) monitors, so I have adjusted the numbers for my setup. Consider using the following numbers (2560, 1440; 5120, 1440) for the 2K resolution and the appropriate numbers for the 4K resolution as well.

Additionally, this guide uses the latest version of AHK - v2. Version 1 is deprecated, and I have modified the code to be compatible with the newer version.

The steps are almost the same:

1. Download AHK v2[www.autohotkey.com]
   
2. Set the following settings for the game:
   
   -ResX=3840 -ResY=1080 (or any other, like 5120 1440 for 2k)
3. Open AHK and start creating a new script:
   
   
4. Name it and create it:
   
   
5. Paste the following code into the created script using any of the editors:
   
   #Requires AutoHotkey v2.0 MoveWindow_Main(width, height) { WinMove 0, 0, width, height, 'A' ToolTip 'Split', width, height Sleep 500 ToolTip return } F9:: { MoveWindow_Main(1920, 1080) return } F10:: { MoveWindow_Main(3840, 1080) return }
6. Start using the script by running it and the game. Use F9 for reverting changes to one monitor (needed for cutscenes etc), and F10 for splitting between two monitors.

You can insert any of the keys you want, instead of F9/F10 (my variant). For example, noirekid is using the numpads:
You can find the full list of keys here: https://www.autohotkey.com/docs/v1/KeyList.htm

Take a look at the screenshots below to see what is the point of this:

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Enjoy!