Okay, as you are only trying to shorten the list, I suggest you use something other than the File Type to select what to show. For a start, when showing duplicates you would want to show the FLAC, MP3, AAC, etc. versions together, so selecting of File Type wouldn't make sense, at least to me.
I suggest you create a Pane type of view using ~dup=[Name],[Album] as the selection criteria, and then set up a Pane Category of Album and set a Group Size of 3. I added a File Type Category so that after select the "J-L" Group, for example, I could easily compare the files, then just select the MP3 files and delete them, if that was my choice. I also added a "File Path" (shown as "Location") Category so that I could easily see where the duplicates were stored, and if they were all in one folder, just select that folder to show only the duplicates, regardless of the file type, and delete the duplicates.
See the attached images for how I set that up.
PS: I haven't found a definition for ~differences either, other than when the function was added back in MC18. But I haven't tried to work out exactly how it would be used. But if you do the above, it won't be required.
23.0.88 (12/6/2017)
5. NEW: Added the smartlist rule "Only differences of" the will find files with different values in the selected fields.