after making a new Music library (Big Sur) in its default location User>Music>Music>Music Library.musiclibrary
- i created a new Music Library.musiclibrary on the external hard drive > inside the old iTunes folder, (you'll have to navigate to your iTunes folder on your external hard drive)
- the Music app created a new folder named ‘Music 1’ & also created a new library there named it ‘Music Library.musiclibrary’
- quit the Music app
to open the new Music Library that contains all of the music do the following,
- navigate to the external drive (make sure it is mounted), then navigate to iTunes>Music 1>Music Library.musiclibrary & double-click the new ‘Music Library.musiclibrary’ file
the Music app will reindex the iTunes folder making your music accessible in the new Music app & also create a new media folder which you can confirm in Music>Preferences>Files>/Your External Hard Drive/music (my folder)/iTunes/Music 1/Media
the old way was to option-open iTunes & navigate to the iTunes folder but this has changed.
now you can just double-click .musiclibrary file located in your external hard drive
verification below: