Touchpad not working after upgrading Debian 9 Stretch

I’ve successfully upgraded my laptop to Debian 9 Stretch but multitouch events like tap-to-click and two finger scrolling doesn’t work anymore. Is this a known problem with the upgrade process?

The synaptic Xorg driver in being superseded by the newer libinput driver, you can read more about here:

You must check the /etc/X11/xorg.conf.d directory that if there is a file like that XX-libinput.conf.

If the directory doesn’t exists, create the directory first:

sudo mkdir /etc/X11/xorg.conf.d

And copy the sample libinput.conf file with the command:

sudo cp /usr/share/X11/xorg.conf.d/40-libinput.conf /etc/X11/xorg.conf.d

then logout the X session and login again.