inb4 duplicate: yes there are many similar questions, but they are either about mouse-acceleration in general instead of specifically touchpad related or their answers didn't solve my problem.
I have tried:
gnome-tweakslets me set the acceleration profile for mouse to "flat", but not for touchpad.
dconf-editoralso provides this option for trackballs, but still not for touchpads.
/usr/share/X11/xorg.conf.d/90-mouse.confas proposed here has no effect
xset m 0 0has no effect
I am using ubuntu 18.04 but I had the same problem on 17.10 as well