Unable to set default values for SynPS/2 Synaptic

You can change the default value in your libinput config file located at

/usr/share/X11/xorg.conf.d/40-libinput.conf

(mine is actually 90-libinput.conf. anyways, something like this.)

Just add

Option "Tapping" "True"

For me, the complete entry is:

Section "InputClass"
    Identifier "libinput touchpad catchall"
    MatchIsTouchpad "on"
    MatchDevicePath "/dev/input/event*"
    Driver "libinput"
    Option "Tapping" "True"
EndSection

See more at:

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

https://www.mankier.com/4/libinput