We have quite a few date objects in the Universe but only some seem to function as a date field whereas some do not.
The easiest way to tell whether a date field is functioning as a date field seems to be to add the date fields as a filter in a query. If it is a proper date field a Calendar option appears. If it is not, no Calendar option appears.
In the screenshot below, the Latest Approved Date functions like a proper date object and shows a calendar option. The other field does not even though it is a date field too.
I'm checking with this forum as the Universe designer didn't have any answer for this.