At the bottom of the Insert page is a dropdown for "Continue insertion with __ rows" -- when using that dropdown to change the number of rows, the datepicker does not appear.
To reproduce, have a table with a 'date', 'datetime', or 'timestamp' column. Go to the Insert page and see that the picker is available. Go to the dropdown and change to any other number of rows. Now look and see the picker is missing.
Note that 'time' columns do behave as expected; the picker is available in every case.
Fixed with https://github.com/phpmyadmin/phpmyadmin/commit/c5796e912f3a43c091706b9592649cf79e4b80a5