Where is the file that handles camera raw thumbnails in Files? I want to add a mimetype (image/x-sigma-x3f) and see what other adjustments I can make. (I don't think it's the file
Maybe a hint for you, I have just been reading this answer explaining how to enable/disable thumbnails by editing the file etc/xdg/tumbler/tumbler.rc
In that file you can see that file types (uri-scheme / mime-type combination) are managed by plugins...