iPod Classic & Apple Music - Manually manage music & missing playlists?

Apple's Music app in Catalina has reduced support for manually managed devices when compared to iTunes. In particular you cannot play or edit content already on the device. Playlists need to be added whole from Music using Finder. If there is content on the device that isn't in your library see Recover media from an iPod - Apple Community. Rebuild your playlists in Music. Then switch to syncing with selected playlists.

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I honestly think that syncing with selected playlists is the easier method. At its most basic you make a list called say My iPod Classic, put what you want into it, and then sync that. Later when you're listening to your library you might run into an album you haven't heard in ages and think, oh, yes let's put that on my iPod, so you add it to the list. When you sync your device it gets added. When you play songs on your classic their play counts get added back into the library. Want to remove something from the iPod? It will be easier to search the playlist in Music (use View > Show Filter Field) than to use the clunky Manage Storage feature in Finder. Take it out of the list and it gets removed next time you sync. Want to create some individual playlists for the iPod? Make a playlist folder in Music, gather all the iPod playlists into it, and sync the whole playlist folder and all of its playlists. That way you can look at the folder to get a clear picture of exactly what gets to go on the device.

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