See here: https://support.microsoft.com/en-us/office/play-music-across-multiple-slides-in-your-slide-show-b01ded6a-28c8-473a-971a-6dfa92cc9367#:~:text=On%20the%20Insert%20tab%2C%20select%20Audio%2C%20and%20then%20Audio%20from,and%20select%20Play%20across%20slides. (That covers the more recent versions of...
15:03 Sun 20th Sep 2020