I have a file: 40-libinput.conf
Section "InputClass"
Identifier "Touchpad"
MatchDriver "libinput"
MatchIsTouchpad "on"
Option "Tapping" "on"
Option "ButtonMapping" "1 0 3"
Option "ScrollMethod" "edge"
EndSection
Section "Inputclass"
Identifier "Trackpoint"
MatchDriver "libinput"
MatchIsTouchpad "off"
Option "ScrollMethod" "none"
EndSection
The key to this is the MatchIsTouchpad lines which differentiate parameters between mouse types.
The Tapping "on" is my preference.
The ButtonMapping is to disable chord emulation of middle button on the TrackPad. Again, my preference
The key to getting middle mouse drag is by disabling the ScrollMethod. The default uses middle button hold to convert mouse movement to scroll events.
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