Do disable the tap do the following:>
- search : TAP
- click on touchpad button
- uncheck "Enable tap-to-click"
and close the window. Your changes will be saved.
Keep in mind that if it does not work as expected, then repeat the steps just to make sure your selections have been recorded. If you cannot get ChromeOS to record your selection or the feature is not working as expected you might want to do a powerwash and try again.