My music is already copied onto new Mac AND into iTunes, but it is not organized into the several hundred playlists I have. How do I get those playlists from old Mac to new Mac (and ensure the songs are placed in the playlists)?
Save a copy of your playlists from iTunes on macOS
You can export a playlist—for example, if you want to save a copy of the playlist, or import it to a different computer so you have the same playlist in both places.
You can also export information about a song (or songs) to use in a database or in another app.
When you export playlists or transfer song information, the actual songs or videos aren’t included—just the information about them or the playlist.
Save copies of playlists or use playlists on another computer
Do any of the following:
Save a copy of a single playlist or use it in iTunes on another computer: Select the playlist, choose File > Library > Export Playlist, and choose XML from the Format pop-up menu.
Import an iTunes playlist: Choose File > Library > Import Playlist. The imported playlist includes only songs and videos already in your iTunes library. Unavailable items are removed from the list.
Save a copy of all your playlists: Choose File > Library > Export Library. The exported information is saved in XML format.
Transfer song information into other applications
Do either of the following:
Export all the song information into a text file: Select a playlist, then choose File > Library > Export Playlist. Make sure Plain Text is selected in the Format pop-up menu (if you use a double-byte language such as Japanese or Chinese, or if the program you’re importing into understands Unicode, you should choose Unicode).
All information from the Info window for each song is exported, not just the fields currently displayed in the library or playlist.
Copy the information (in the columns that are visible) for one or more songs: Select the songs and choose Edit > Copy, and then choose Edit > Paste in another application (for example, an email or text document).