Hi, I use Debian SID, which comes with the latest version of LxInput: 3.0.5-1
Unfortunately, changes made to the program in relation to the mouse speed have no effect.
To solve the problem, I installed version lxinput_0.3.5-1+rpi14, fork of Raspberry Pi OS available at https://archive.raspberrypi.org/debian/pool/main/l/lxinput/
They made several changes to the source code: https://github.com/raspberrypi-ui/lxinput