Created attachment 147925 [details]
all tapping options inactive (regardless how often it's started from start menu).

SUMMARY
Tapping options are most of the time inactive when starting systemsettings / touchpad configuration. The problem could be seen (long?) before 5.24.4.

STEPS TO REPRODUCE
1. Start systemsettings from the start menu.
2. Go to touchpad configuration
3. 

OBSERVED RESULT
Tapping options are disabled

EXPECTED RESULT
Tapping options should be enabled.

Further investigation:
Started kcm_touchpad from konsole. After the first startup, the result is the same as described above. Starting it twice (after the first run has been closed), suddenly parts of the tapping options are active. Closing it and starting it again reveals the same problem as it could be seen from beginning: all tapping options are inactive. This behavior is stable from now on - even after the n.th start.

Next try:
Starting kcm_touchpad in the konsole, but changing the LANG variable:
export LANG=C
=> now it's working as expected.

Usual LANG configuration here is:
~> locale
LANG=de_DE.UTF-8
LC_CTYPE="de_DE.UTF-8"
LC_NUMERIC="de_DE.UTF-8"
LC_TIME="de_DE.UTF-8"
LC_COLLATE="de_DE.UTF-8"
LC_MONETARY="de_DE.UTF-8"
LC_MESSAGES="de_DE.UTF-8"
LC_PAPER="de_DE.UTF-8"
LC_NAME="de_DE.UTF-8"
LC_ADDRESS="de_DE.UTF-8"
LC_TELEPHONE="de_DE.UTF-8"
LC_MEASUREMENT="de_DE.UTF-8"
LC_IDENTIFICATION="de_DE.UTF-8"
LC_ALL=

I attached some screenshots as example:
touchpad-tapping-inactive-1 => all tapping options inactive (regardless how often it's started from start menu).
touchpad-tapping-active-after-second-start => all tapping options active on second start on konsole
touchpad-tapping-partly-active => tapping options partly active after all following starts on konsole
touchpad-tapping-active-LANG=C => tapping options active while using LANG=C on konsole

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.24.4
KDE Frameworks Version: 5.92.0
Qt Version: 5.15.2