Change date format "Authored on" for views with replacement pattern
In Drupal 8, fields use the normal field formatters.  In your list of Fields in the View, click on Content: Authored on (Authored on).  You can change the Formatter to what you want (same choices as Manage Display on the content type configuration).  You can then configure other options, like the format.

If you already are using {{ created }} in the template, and you need it in a different format for a replacement pattern / token, then add Content: Authored on (Authored on) again to the list of Fields, but exclude it from display.  Reorder things, so this appears before the field you need it as a token.  Configure it as above.  Then, where you need the token, you should have {{ created_1 }}, which is the duplicate you just made.