How to disable Magic Mouse horizontal scrolling?
Note: I did not invent this solution but found it elsewhere on the Web.
Open a Terminal window (via the Utilities folder), enter:
defaults write com.apple.AppleMultitouchMouse MouseVerticalScroll -bool NO
and hit RETURN. Then, using the slider on the mouse, power the mouse OFF. Confirm that it's off, then power it ON. Close the terminal app.
I know the command refers to vertical scrolling, but it seems to have done what I needed it to do: disable horizontal (left-right) scrolling while retaining vertical (up-down) scrolling. At least it worked for me on a Mac M1 running Monterey 12.6.1.
The question was asked previously but the poster said it didn't work. That was probably because he did not switch the mouse off and on after entering the command.
Apple: This should really be accessible via a control panel. No user should HAVE to fix things using the Terminal app.
iMac 21.5″