I was looking for Create Custom Format. Which is there but I did not see it
Okay, let’s try again, step by step.
Open the document you want to format the dates in.
Click on any cell. Look to the
top right. Do you see the buttons with
Format and
Organize below them? If yes, click on the
left button (above
Format) if not already selected. The sidebar should expand.
The sidebar should have
Table, Cell, Text, and
Arrange for headers. Click on “
Cell.”
The first entry that comes up will be “
Data Format.” Below it, labeled “
Automatic,” is a dropdown button to expand a list of choices. Click on that button, to reveal your choices.
From the list, scroll down with the cursor and select “
Date & Time.” Right there, you can set up the formats for date and time. We may not be running the same version of macOS. I have Sequoia 15.3, so our versions of Numbers.app may have some differences. But this is the way I remember doing it ever since I started using Numbers (God knows how many) years ago.