What is playback in the Mac Music application? How do I disable playback?

Once in a while when I select (click on) a song that is in my Music library - I do not have a Music subscription - I get a message saying "You are about to start playback. Do you want to clear the song previously added to Playing Next?" and I'm given the option of "Clear Song", "Play Song" or "Cancel". I don't know what this is, and don't want it, but I can't get rid of it. Every time I click on a song I see the same message. How do I disable this - forever, ideally!