Where are changes in the Apple Music player saved when using the iTunes.itl as library for the Music Player

In macOS 10.15 Catalina and later the Music Library.musiclibrary file is a package that contains equivalents for the library files that would previously have been in the iTunes folder. Internally there is a file called Library.musicdb, which would appear to be the real analog to the .itl file. Music creates Temp File.tmp files within the .musiclibrary package when updating the library, so it is possible that in a corrupted library there will be a .tmp file that can be restored if you right click on Music Library.musiclibrary and Show Package Contents. If restoring a .musiclibrary package from Time Machine you should option-start Music and explicitly select the restored file.

If your library is in a non-standard location another possibility is that the preference file that records which .itl file to open has been reset or corrupted. This may cause iTunes to open or create a library at the standard path of <User's Music>\iTunes. In this event, press and hold down shift/option as you launch iTunes to reconnect to the correct library file.

In a similar vein it is possible that a corrupt preference file may cause iTunes to fail at launch with one of these errors:

• The file iTunes Library.itl cannot be read because it was created by a newer version of iTunes.
• The folder “iTunes” is on a locked disk or you do not have write permissions for this folder.
• The iTunes Library.itl cannot be found or created. The default location for this file is in the 'iTunes' folder in the 'Music' folder.

It may be worth trying the shift-start-iTunes method (option on a Mac) to actively select the .itl file that should contain your library. If you still get the error message try Repair security permissions for iTunes for Windows and/or check for interference from anti-virus software.

The default location for a Music library in Catalina and later is ~/Music/Music with the media files consolidated into ~/Music/Music/Media. After importing your iTunes library you may want to copy your active Music Library.musiclibrary file into ~/Music/Music replacing any older copy there, then use Music > Preferences > Files to reset the media folder path, and File > Library > Organize Library > Consolidate Files to bring all the music into media folder. You can then remove the originals from the old iTunes Media folder. Repeat with TV as appropriate. Alternatively you could create the nested layout of library folder and media folder on an external drive.

See Managing your Mac media libraries - Apple Community for more on reorganizing old iTunes content for the new apps.

For more info, see:

Empty/corrupt iTunes library after upgrad… - Apple Community

Move your iTunes library to a new computer - Apple Community

To be clear, when you use Music to open a .itl file it will convert to a .musiclibrary package which is then used thereafter. If you reopen and convert the .itl file all the changes made in Music will missing from this newly converted library. The only way to reliably have the same library, ratings, play counts, playlists, etc. on the two different builds of macOS is to have an active subscription to either Apple Music or iTunes Match such that updates made in one library can sync automatically to the other via the cloud. If that isn't an option, e.g. library over 100,000 tracks, or cost, then you should made all edits in the Mojave system, which you can clone for use in Sequoia knowing that any changes made on the Sequoia system are going to be lost next time you copy over the .itl from Mojave.

tt2