Random zoom on iMac screen

it sounds to me like you have discovered "smart zoom". When active, if you lightly double tap your Magic Mouse, the screen will zoom in or out. It is very sensitive, and you may not notice that you double tapped. you can go into System Settings > Mouse in the "point & click" tab and turn off "smart zoom". (if you are using Monterey and before, the preferences panes will look different, but the setting is still in the "mouse > point and click" section)

then the unexpected zooming should stop. but if smart zoom is the cause, you may want to get used to how it works. since I started using it, I have wondered how I ever lived without it.

[Edited by Moderator]

Refer to View a larger version of colors or text you’re reading or typing on Mac - Apple Support or general Accessibility settings.