Quote from https://help.gnome.org/misc/release-notes/3.28/
-
All touchpads now use a gesture for secondary click (the equivalent to right click on a mouse) by default. To use the gesture, keep one finger in contact with the touchpad and tap with another finger. In many cases this replaces tapping areas of the touchpad as the default secondary click method. A choice between the two behaviors is available in the Tweaks application.
