I always ride with this option switched off.
I almost never pan the map (too complicated while riding).
If I do not touch the ZoomIn/Out buttons the app dynamically zooms in when I get closer to a turn and zooms out afterwards automatically.
If I ZoomOut or ZoomIn manually, the zoom level remains as I set it.
To reactivate the dynamic zooming on turns, you have to press the “crosshair” button, as @Guenther explained above. That works.