I have now nuked Opera completely after I have saved all bookmarks and thumbnail pictures before.
Then I reinstalled the newest version. When it worked I manually recovered all settings and imported the bookmarks.
It seems as if Opera update doesn't work properly when you use Opera a certain time and automatic update has updated it many, many times.
I hope updates in the future will not cause so much anger again.
In the past I had similar problems after a Windows update for Intel/ Nvidia (I don't know which of both was the trouble maker). But it is much more nasty when the system is damaged, not only the browser.