I’ve done the full reinstall: new wordpress, new database, new theme. There are no plugins active.
I am still not able to create a dynamic sidebar. If I create one, for exampe “Home Full Screen”, then go to appearance>widgets, there I can see the “Home Full Screen” widget. When I go back to appearance>theme options and create another sidebar, then go back to appearance>widget, the “Home Full Screen” is overridden by the new created sidebar.
I have switched theme. The widget menu excists also in the theme twenty fifteen, but the sidebars don’t.
Could this have to do with a recent WordPress update?