Turn off Slideshow music in photos
I would like to play a slideshow of videos without music. The canned Apple music is distracting
iMac Line (2012 and Later)
Just don't add any music to the slideshow when you create it. Or, choose something you actually like.
Instead of Play Slideshow, choose Create > Slideshow > Photos and choose the music you want or nothing (click the Note icon).
Update: From Play Slideshow, you can disable the music by selecting Music, Select song, deselect song.