Ah, I have found the error:
My link to the pages in the backend was:
index.php?option=com_sppagebuilder&view=pages&filter[category_id]=32
that led me (as you can see in the video) to a probably older pagebuilder page view. The whole thing doesn't work above that.
But if I use the following link:
index.php?option=com_sppagebuilder&view=editor&tmpl=component#/pages?filter=%7B%22category%22%3A%2230%22%2C%22limit%22%3A%2215%22%2C%22sortBy%22%3A%22title%22%7D&page=1
then the view of the pages looks like yours and I can actually set everything as desired and the user can edit his pages.
Maybe you can somehow remove this old view so that you can't get there by mistake.