Make the cell wider?

Beege

Widen the column.
Change the font to something smaller.
Change the number format so that the formatted date is fewer characters.

The #'s indicate that the cell (column) is not wide enough to show the
answer or that there is an invalid date in the cell. You can widen the
column by clicking on the dividing bar to the right of the column header and
dragging until the #'s change. The cursor will change to a bar with a left
pointing and a right pointing arrow when it is on the dividing bar between
the column headers. If the #'s remain, it means the cell has an invalid
date.

Tyro