Cannot create new events by clicking in the calendar widget

It used to be the case that one can create a new events by clicking on an empty space in the calendar widget.

Since XWiki 13.x seems no longer to work (it still works with XWiki 12.8).

Instead one need to click the "create new event button" to create a new event. Of course then the start date is not prefilled.

Also the date picker for the start and end date fields is missing.

If one looks in the browser console, this lists a bunch of 404 errors when trying to load resources that are indeed not present, starting with  /xwiki/bin/skin/skins/flamingo/uicomponents/widgets/datepicker/calendarDateSelect.css.