RSS

 This snippet is an example config for a date format in Drupal which can be imported.

langcode: en
status: true
dependencies: {  }
id: rss_feed_date_format
label: RFC822
locked: false
pattern: 'D, d M Y h:i:s O'

Change the date format via Sitebuilding
In the administrative menu open Configuration -> Region and language -> Date and time formats or open the path /admin/config/regional/date-time.
Then use the button "+ Add format".

Here you can give your new date format a label and enter D, d M Y h:i:s O as a fitting RFC822 <pubDate> format.

For more information about PHP date format options, see the official PHP documentation.