"Exporting iTunes displays from old iMac to new MacMini: I've exported the music data (iTunes Library, &c.) from the old iMac, and the data is available when I open Music in the Mac mini, but not displayed as it was in Tunes, i.e. with playlists organized under composers, &c. How can I get Music to organize the data as it was organized in iTunes?"
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Transferring Music as it was to an New Mac:
iTunes was discontinued on the macOS a long time ago. Apple Music is what is on nowadays' macOS versions. iTunes still stands as the player of iTunes Store music for Windows PCs.
1. Export your Music Playlists from the olde Mac
Then...
2. Import your Music Playlists to the new Mac
Find Out how to here: Save a Copy of a Playlist in Music on Mac - Apple Support