Ok since I cannot remove xf86-input-synaptics, I tried to get TrueOS to use xf86-input-libinput by creating the following symlink:
$ ls -l /usr/local/etc/X11/xorg.conf.d
lrwxr-xr-x 1 root wheel 49B Jul 6 19:11 40-libinput.conf -> /usr/local/share/X11/xorg.conf.d/40-libinput.conf
-rw-r--r-- 1 root wheel 823B May 20 01:23 wacom.conf.sample
It still doesn't seem to be using libinput.
$ grep "Using input driver" /var/log/Xorg.0.log*
/var/log/Xorg.0.log:[ 39.879] (II) Using input driver 'kbd' for 'kbdmux'
/var/log/Xorg.0.log:[ 39.884] (II) Using input driver 'mouse' for 'sysmouse'
/var/log/Xorg.0.log.old:[ 40.179] (II) Using input driver 'kbd' for 'kbdmux'
/var/log/Xorg.0.log.old:[ 40.184] (II) Using input driver 'mouse' for 'sysmouse'
Now I'm confused. Which is this driver
mouse that it is using? Shouldn't that be synaptics by default?