Widgets cannot be inserted

Hi,
although I did the following steps (as adviced in another thread) I am not able to insert any widget into an Elementor template section. Drag and drop doesn’t work and the respective menu item within the section is deactived.
The steps I did are:
– All plugins deactived,
– Permalinks saved,
– Switched from child-theme to parent theme,
– Php Version is > 7.

The page I need help with: [log in to see the link]