Synaptics touchpad tap-to-click is not working in Ubuntu 16.04 LTS (Gnome)

I've found a permanent solution with this command

gsettings set org.gnome.desktop.peripherals.touchpad tap-to-click true  

Gnome starting at 3.20 only allows configuring devices using the libinput driver. So if you are not using the libinput driver, it won't show up in the GUI.

Comment from discussion gnome 3.22 still does not detect tap to click?.

Additionally, GNOME may override certain behaviors, like turning off Tapping and forcing Natural Scrolling. In this case the settings must be adapted using GNOMEs gsettings command line tool or a graphical frontend of your choice. For example if you wish to enable Tapping and disable Natural Scrolling for your user, adjust the touchpad key-values like the following:

gsettings set org.gnome.desktop.peripherals.touchpad tap-to-click true  

https://wiki.archlinux.org/index.php/Libinput#Touchpad_not_working_in_GNOME

In 18.04 (with Unity 7) I had to install the synaptics driver:

sudo apt install xserver-xorg-input-synaptics