"both both halves of the screen showing the exact same thing."
That's not what we call display spanning. So for this an ordinary HDMI splitter will show the exact thing on both displays. I think you need to clarify your goal.
Hello, I have been searching around the internet for a solution to my problem, but most solutions involve downloading dodgy programs to get this to work (I don't mind downloading programs, I just need to know that they're safe!)
Basically, what I want to do is to split my monitor screen into two parts, with both halves of the screen showing the exact same thing. As an example, having a game displaying the visual feedback on both halves.
Any help would be really appreciated on this.

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