https://gitlab.com/kaushalmodi/hugo-theme-refined/blob/2b74499733215ec95dc9a6fb11cfffcc1a42861a/layouts/partials/publishdate-maybe.html#L1

hugo-date-format

{{ dateFormat .Site.Params.DateForm (default .Date (.PublishDate)) }}
<!-- Above is the optimized version of below, thanks to https://discuss.gohugo.io/t/how-to-use-the-publishdate-if-both-publishdate-and-date-are-set-in-frontmatter/5142/3?u=kaushalmodi  -->
{{/* with .PublishDate */}}
    {{/* if eq ($.PublishDate.Format "2006-01-02") "0001-01-01" */}}
        <!-- Print the Date instead of PublishDate if PublishDate is defined but at its initial value of Jan 1, 0001 -->
        {{/* $.Date.Format $.Site.Params.DateForm */}}
    {{/* else */}}
        {{/* $.PublishDate.Format $.Site.Params.DateForm */}}
    {{/* end */}}
{{/* end */}}

new_gist_file_1

 The layout string used by the Parse function and Format method
// shows by example how the reference time should be represented.
// We stress that one must show how the reference time is formatted,
// not a time of the user's choosing. Thus each layout string is a
// representation of the time stamp,
//    Jan 2 15:04:05 2006 MST
// An easy way to remember this value is that it holds, when presented
// in this order, the values (lined up with the elements above):
//      1 2  3  4  5    6  -7

{{ .Date.Format "Jan 2, 2006" }} becomes “Oct 4, 2007”
{{ .Date.Format "Jan 02, 2006" }} becomes “Oct 04, 2007”

https://www.madboa.com/blog/2016/08/24/hugo-dateformat/