I have the same need and agree with Kevin Linden’s interpretation of the original question/issue.
Several Lightbox plugins create a full size image lightbox display for existing basic WP Galleries, but require that the the gallery link be set to media file.
I want my Simple Lightbox plugin to be active/enabled for all my WP galleries.
With recent updates, I must change every new gallery link value to media file in order for the Lightbox plugin to work for that gallery.
And of course I frequently forget to do this… I want to change the default value from “none” to “Media File”.
With previous versions of WordPress we were able to modify the default value by editing https://sitename/wp-admin/options.php, but this no longer works (when I look at options.php ‘image_default_link_type’ is set to “file”, but the default for all images & galleries is “none”).