How can I horizontally flip/invert my monitor (not rotate)?

I had the same need for a content displayed within a browser, where I ended up using CSS tip to flip the element :

    transform: scaleX(-1);

Not sure it applies to OP situation, but could help others.

I know exactly what you are trying to achieve. I'm running a three display setup in Windows extended desktop mode where one of the displays is in a teleprompter and needs to be horizontally flipped (left right flip) so that the mirrored reflection is the correct orientation.

Of the software options I investigated only Ultramon can do this. However, it can't do it in the extended windows display mode, it switches to duplicating the same monitor.

There are two hardware products that can do this: HDMI Mirror Box and the Decimator MD-HX. I've owned both.

• The HDMI Mirror box defaults back to the original settings each time it is powered off and it is confusing for end users to reset properly. Further, mine stopped working after 18 months (the warranty period is one year).

• I've just purchased the Decimator MD-HX and the Horizontal Flip parameter in the Scaling settings will do what you want. Further, the MD-HX is a vastly superior build quality to the HDMI Mirror box in my opinion and it autosaves the settings so that when it is powered off and restarted it maintains the settings you want. It also has a very useful USB connection and software interface where you can update the firmware and access all the settings menus.

For the sake of transparency, I have no association or commercial interest in any of these products.