Make image files with missing or incorrect file extensions still work with modern Drupal 8 9 10
- drupal 8 add image extension based on mime type
A cool core issue about this (closed as duplicate but it looks more like it acted as the ‘meta’ grouping issue): Allow image effects to change the extension [#2341251] | Drupal.org
https://www.drupal.org/project/drupal/issues/2311679
Contrib module for figuring out mime type from file extension: https://www.drupal.org/project/sophron