Options > View:
I suspect your Zoom Scale factor is set to 1.0
Try 0.9 or 0.95
A value larger than 1.0 (like 1.05 or 1.1) will reverse the zooming direction of the wheel.
Stranger and stranger. This morning, the Scroll Zoom works normally once
again. I tried it first on a file from some weeks ago (Scroll Zoom
worked immediately) then on a problematic file I saved yesterday.
Scroll Zoom worked again. Maybe opening the old file healed the code.
For several days I have been receiving promotional messages, inside
Rhino, for a particular pop-up. Might be the source of the problem.
If I lose scroll-Zoom again I will re-install Rhino 5.
I’d also check the Windows Control Panel for your mouse settings. There, you can modify the buttons and wheel settings. My mouse lets me set the speed of the scroll wheel, so yours could have been modified accidentally / corrupted / etc.
And … maybe even update the mouse driver if needed. Some gamer mice (like mine) have driver updates occasionally.