Adopted from: https://techinfluence.net/turn-off-mouse-acceleration-on-mac/#Method_2_Turn_Off_Mouse_Acceleration_Using_the_Terminal
Check the current value of scaling in user defaults:
~ defaults read .GlobalPreferences com.apple.mouse.scaling
This will display a hidden preference setting that you can change by altering the number at the end. If the mouse acceleration feature is enabled, the above command should display a value between 0 and 3. This is the value that is altered when you move the ‘Tracking Speed’ slider
Disable mouse acceleration: