xinput advanced configuration - Ubuntu 20.04

Great lines, worked for me

xinput set-prop "Microsoft Microsoft Trackball Optical®" 157 2 0 0 0 2 0 0 0 1
xinput set-prop "Kensington      Kensington Expert Mouse" "libinput Scroll Method Enabled" 0, 0, 1
xinput set-prop "Kensington      Kensington Expert Mouse" "libinput Button Scrolling Button" 3
xinput set-prop "Kensington      Kensington Expert Mouse" "libinput Accel Speed" 0.7
xinput set-prop "Kensington      Kensington Expert Mouse"  "Coordinate Transformation Matrix" 2.000000, 0.000000, 0.000000, 0.000000, 2.000000, 0.000000, 0.000000, 0.000000, 1.00000
xinput set-prop "Kensington      Kensington Expert Mouse" "libinput Natural Scrolling Enabled" 1

Coordinate matrix affects - speed

Scrolling button - make a button enable scrolling

Other useful commands

xinput set-props 9

Note that if you add commands to startup - refer to the input device and property by name, not by id