I am using MATE Ubuntu 18.04 LTS, I clumsily keep accidentally simulating the middle click by simultaneously clicking the left and right click, I really want to disable it, I can not see the option in the touchpad settings. Please help.
you can use gsettings or dconf-editor to disable this function..
to get the value, use
gsettings get org.mate.peripherals-mouse middle-button-enabled
to set the value to false, use
gsettings set org.mate.peripherals-mouse middle-button-enabled false
Dconf-Editor (If not installed,
sudo apt install dconf-editor)