This is intentional from the good GNOME folk who developed 3.28
The default is now the two fingered tap on the touchpad. This is the Mac method and fixes touchpad sensitivity issues.
To revert to using your actual touchpad areas/buttons, you either use gsettings/dconf:
gsettings set org.gnome.desktop.peripherals.touchpad click-method areas
And to re-enable two finger tap:
gsettings set org.gnome.desktop.peripherals.touchpad click-method fingers