@brahma Thanks that brought me to the right direction!
I remember that I already tested with modprobe -r and found ‘hid_multitouch’ that is mentioned in other threads as well. But that doesn’t change the behavior, so I tested a bit through the lsmod modules. Especially when grepping for ‘wacom’ instead of ‘touch’, I found that two modules are used for the pen detection. I couldn’t test it long already but as the pen is recognized before blacklisting and afterwards not any more and the ghost touches are gone, I am sure that I finally found it.
What i did if anyone has the same issue with (mostly Thinkpad Yogas) with both touch and pen:
Temporary deactivated the modules ‘wacom’ and ‘usbhid’ like so
sudo modprobe -r usbhid
and after that worked to make it persistent I made a file /etc/modprobe.d/wacom.conf:
blacklist wacom
blacklist usbhid
Interestingly, the hid_multitouch module doesn’t need to be deactivated for the device to disable the touch functionality as well.
And even if usbhid sounds like affecting more devices, it does not seem so: Touchpad, Pointer, Keyboard is still working.
So I think its solved now. Thanks again for the inputs, I was totally centered to the xorg methods to oversee the obvious.