De link :
You can disable left+right click acting as middle click for all devices system-wide by adding the file /etc/X11/xorg.conf.d/20-3rdbutton.conf with the following content:
Section "InputClass"
Identifier "middle button"
MatchIsPointer "on"
MatchDriver "libinput"
Option "MiddleEmulation" "off"
EndSection
Adapted from the following Stack Exchange answer: https://unix.stackexchange.com/a/284782