org-popup-calendar-for-date-prompt

org-popup-calendar-for-date-prompt is a variable defined in `org.el'.
Its value is

t

• This variable is an alias for `org-read-date-popup-calendar'.

Documentation:
Non-nil means pop up a calendar when prompting for a date.
In the calendar, the date can be selected with mouse-1. However, the
minibuffer will also be active, and you can simply enter the date as well.
When nil, only the minibuffer will be available.

You can customize this variable.