Mouse speed setting not working under macOS Tahoe

[TrevorBurnham]

On a new Mac running macOS 26.1, I found that the mouse speed setting is now a no-op. E.g. setting

defaults write NSGlobalDomain com.apple.mouse.scaling -float 3 && killall Dock

no longer increases my mouse speed. Conversely, I increased the tracking speed through System Preferences and it had no effect on that value, or any other value in the global domain.

I would guess that com.apple.trackpad.scaling has the same issue, though I haven't confirmed yet.

I found this reported here, but I haven't been able to find a solution: https://discussions.apple.com/thread/256127096?sortBy=rank

[TrevorBurnham]

I did some investigating and found that writing to this preference changes the mouse speed:

# For any value between 0 and 3
speed=3
hidutil property --set "{\"HIDMouseAcceleration\":$((speed * 65536))}"

So for instance,

hidutil property --set '{"HIDMouseAcceleration":196608}'

gives you speed equivalent to the maximum slider in the Mouse preference pane.

Maddeningly, though, the Mouse pane in System Settings doesn't reflect this change: Mouse movement speed changes, but the slider still shows the old value, even after restarting System Settings. So there's a piece missing…