When I tried uninstalling yaourt first, the system threatened me it would remove hundreds of packages with it. That’s why I didn’t remove yaourt.
So I now tried ‘pamac update -a’ from the Update-Threat. It gave me the list of potential changes to be performed, but I did not yet commit changes. Instead I opened the graphical package manager again, and tried removing yaourt for checking which dependencies this would kill again. Strangely there where no further dependencies this time, so I removed yaourt. It seems as ‘pamac update -a’ had fixed the problem without me actually having commited the changes it announced!
After this the graphical update allowed me to update, and it’s running now, with 310 packages to go.
I will update you about the results!
Systems wants to reboot now! See you! (I hope )
System is back again, now wants to install a new Kernel.
OK, everything seems to be working. Also I can install packages again.
If only I had a clue what happened right now…