This setting is disabled for some reason:
In my research on this, it sounds like I need synaptics driver versus libinput, but I can’t find either package.
You need the xserver-xorg-input-synaptics package.
It was already installed. Do I need to enable it or something?
It should be running automatically with the package installed. But maybe the synaptic driver does not support your hardware than it falls back to libinput.
There is a whole wiki article with plenty of things to try out: https://wiki.debian.org/SynapticsTouchpad