First check whether the synaptics driver is installed -
apt-cache policy xserver-xorg-input-synaptics
If it doesn’t show as installed,
sudo apt install xserver-xorg-input-synaptics
I don’t remember if a reboot is needed at this point, but definitely you’ll need to at least log out & log back in log into an Xorg session - not a Wayland session.
When I was seeking this on one of my own systems, this was enough to get it working for me. You can check that it works for you by looking for the Synaptics properties in the output of
xinput list-props 'ETPS/2 Elantech Touchpad'
For (1) this might be an alternative to switching to the synaptics driver. For what it’s worth, I switched to use that method on my main system for my USB touchpad, and setting touchpad sensitivity how I wanted ended up physically measuring the size of my touchpad and entering the real actual dimensions in the suggested command.