Fujitsu E5511 onboard keyboard not working after grub

In the running system on a Fujitsu E5511 laptop there is no working keyboard.

I installed as usual from an USB stick with no problems. Onboard (intern/native) keyboard worked as expected.
After final reboot it was not possible to type the password into the SDDM Login Screen, only mouse and touchpad did work.

Some tests I did:

  • External USB Keyboard works (impractical workaround)
  • Boot into runlevel 3 doesn’t help
  • Some posts on the internet for ubuntu or fedore about this problem didn’t help me

Is there a solution that I haven’t found?
What information do you need to help me?

Would be grateful for help
Regards

Try different kernels, in particular, the basic GA kernel which should match the one on installation medium.

It may give others some ideas how to proceed. What about posting links to these posts as long as you already have found them?