This doesn't work. Mouse acceleration isn't exposed using a defaults key anymore. You need to use a tool like linear mouse to modify the scaling value.
In the before-times, in the long-long-ago, we could modify basic system settings from a nice discoverable GUI control panel. Why is the future year of 2022, no doubt filled with flying cars and personal jetpacks, continually found to be unable to deliver features we took for granted in 1995?
This simply hasn't worked for me in years. Haven't tried in about a year, though.
Its not enough, you need a program called USB Overdrive, it completely fixes the issue
So you need a third party tool to make an official device work properly?
This helps, but does not actually result in a flat acceleration curve.