Check to see if you have xorg-xinput installed: pacman -Qs xinput
Install it if you don’t have it
xinput
- this will give a list of your devices. Find the number for your touchpad. You’ll need this later
xinput list-props N
- N being your device number
Now the hard part. One or more of these may be about clicking, tapping, etc. The names will be vendor specific AFAIK. Let’s assume you find one for tapping, and it’s 0, meaning off. Find it’s ID, then use xinput again:
xinput set-prop N ID 1
N = device
ID = the numbers in parens in the list-props list.
If it works now, save that last xinput command, and put that in a place where you launch other startup programs for Cinnamon.
How’d this get unset? Not clear. It’d depend wholly on what your last update did. These shouldn’t get overwritten, but perhaps a driver change/move for your device did it.