Просто добавьте:
Option "ClickPad" "true"
Option "EmulateMidButtonTime" "0"
в /usr/share/X11/xorg.conf.d/50-synaptics.conf
Что-то вроде этого:
Section "InputClass"
Identifier "Default clickpad buttons"
MatchDriver "synaptics"
Option "ClickPad" "true"
Option "EmulateMidButtonTime" "0"
Option "SoftButtonAreas" "50% 0 82% 0 0 0 0 0"
Option "SecondarySoftButtonAreas" "58% 0 0 15% 42% 58% 0 15%"
EndSection