Is there any way to mirror only the secondary monitor?
Yes. With the secondary monitor open, click on the mirror buttons at the bottom of the secondary monitor’s projection. Note that the buttons may appear semi-transparent while the printer is prompting. This is done not to distract the reader. The buttons will also mirror with the projection, while staying in place.
Hope this helps!
Here’s a screenshot of what that looks like:
Individually Flipped Projection