The touchpad on my new Ubuntu 18.04 LTS laptop was frozen. Toogling 🖱 with
<Fn>-<F4> didn't worked.
- Logout: didn't work at all
- Reboot: worked most of the time
After changing the Mouse Click Emulation in Keyboard & Mouse in Ubuntu Tweak from the default “Fingers” (2 fingers for right click; 3 fingers for middle click) to “Area” (Right/middle click determined by clicked area), one might have to wait for next reboot.