Not quite related, but something I learned just now trying to search Apple Music behaviors: toggle “infinity” play on or off if you do or don’t want Music to add more music automatically after a playlist or album. This probably explains what happened after the Harry Potter soundtrack ended: infinity mode continues with same-genre music.
How to stop Apple Music autoplaying extra songs
Sick of those 'similar' songs tacked on to the end of an album or playlist? Here's how to turn off Apple Music's autoplay feature
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