Picture-in-picture Zoom - How to Adjust Magnification (Not Size of Box) in Big Sur OS

Low Vision Accessibility on Apple Products

Hi All.

I've upgraded & most things are working well but I cannot find a way to adjust the picture-in-picture zoom display. I can adjust the size of the actual box itself by selecting the advanced then pressing adjust size & location button.

What I can't do is make the magnification of what is inside that box any bigger - it makes the text a tiny bit bigger, but not big enough. I seem to remember a previous OS having a scale that could be adjusted manually to allow the text within the box to be enlarged. Anyone know how to do this on Big Sur?