sub-classes of mime types aren't handled, which prevents the creation of djvu thumbnails
Originally, an issue was filed against evince here because evince-thumbnailer 42.2 fails to create thumbnails for djvu files.
The issue seems to be caused by the fact that the mime type evince uses to identify djvu files was changed from image/vnd.djvu+multipage
to image/vnd.djvu
, and the fact that gnome-desktop doesn't handle subclasses of mime types, as explained in this comment.
Therefore, this was determined to be a bug in gnome-desktop (presumably).
The issue occurs on Fedora 36 Workstation.