Comment 14 for bug 1826597

I though I might experiment a little. I installed xubuntu-desktop with the lightdm display manager. Didn't work either. Then I installed kubuntu-desktop with sddm display manger and the suddenly my touchpad started working.
I then did a dpkg-reconfigure gdm3, rebooted and logged back into the "standard" gnome session. And now my touchpad is working with the Nvidia drivers installed and working. I have no clue why but, to resume, there are 2 workarounds:
1: use nouveau drivers instead of nvidia
2: install kubuntu-desktop (and log into ubuntu-desktop or whatever floats your boat).

This also indicates that it's "just" a config issue somewhere.