I would to change the date format when modifying an event in Calendar. Currently, Calendar shows the date as 12/10/2020 when I go to modify the date/time. This is the same as is displayed above the calendar preview in System Preferences → Date & Time.
My formats in System Preferences → Language & Region → Advanced... → Dates are the following:
Short : 2020-06-01 Medium : 01 Jun 2020 Long : 01 June 2020 Full : Monday, 1 June 2020
Calendar seems to be using the Medium format when creating a new Event. In Calendar, if I right click → New Event, the date is displayed as
10 Dec 2020 13:00 to 14:00.
However, when I click on that line to modify the date/time, the window changes to
starts : 12/10/2020 13:00 ends : 12/10/2020 14:00
Where is Calendar getting the format of month/day/year from? In Calendar → Preferences, I could not find a way to change this, as the only preferences there are things like the Days per week, Start week on, and how many hours to display at once.
I am on macOS Catalina 10.15.7.