With xf86-input-libinput, turning off the "Disable touchpad when typing" option in the "Enable/Disable Touchpad" tab seemingly has no effect, as demonstrated by xinput list-props not changing. It appears that libinput integration in general is quite poor, as quite a few options are greyed out. Furthermore, the version of systemsettings which I'm using (5.8.4) is not even listed as an option in the bugtracker. Is this software unmaintained?
Same here on openSuse Tumbleweed, using plasma 5.10.3. I would like to enable 'disable touchpad while typing' but the setting makes no difference. Taps are still detected which can be frustrating.
As you have discovered, Libinput support here is poor to nonexistent. Fixing that is tracked with https://bugs.kde.org/show_bug.cgi?id=383379 As a workarounfd, you can either remove Libinput or configure it via .conf files if you're using Xorg: https://wiki.archlinux.org/index.php/Libinput#Configuration *** This bug has been marked as a duplicate of bug 383379 ***
Libinput support is currently only active in Wayland. This setting works fine in the Wayland version, but we can't access it from X11 yet. Duping this to *** This bug has been marked as a duplicate of bug 387153 ***