I've installed 18.04 on an Alienware laptop. The Synaptics touchpad shows in /proc/bus/input/devices as well as xinput list (SynPS/2 Synaptics TouchPad).
I've installed xserver-xorg-input-synaptics. xinput --list-props for the trackpad shows a Synaptics driver. Touchpad is turned On in settings.
The touchpad lights up when I touch it (because everything has to be rgb on this thing), but it does nothing to the cursor, and the buttons don't do anything either.
I've seen answers involving updating the kernel. I've tried that, and then the whole thing fails to boot, so I'm looking for any answers that don't involve updating the kernel. Currently on 4.15.0-43-generic.