Restrict the media library modal to display only supported images

[enricobattocchi]

We should research if there is a way to restrict the media library modal to display only the images in a subset of formats, namely JPG/PNG/GIF/WEBP, to make it easier for people to select a supported image when e.g. choosing a social media image in the metabox or in the settings.

[enricobattocchi]

We could use this filter: ajax_query_attachments_args
The $query array should probably be something like this:

array (
  'post_mime_type' => 'image',
  'orderby' => 'date',
  'order' => 'DESC',
  'posts_per_page' => '80',
  'paged' => '1',
  'post_type' => 'attachment',
  'post_status' => 'inherit,private',
)

so editing the post_mime_type value would do the job
the problem is: we should apply this only to the social media case, and not interfere with thumbnail or content images selection.

It looks like ACF adds something to the $_POST array to make it easier: https://support.advancedcustomfields.com/forums/topic/filter-gallery-items/
They do it here

[pls78]

I also found this filter.