macOS may require permissions to be set for Serato DJ Pro or Lite, to access your Music app's 'media library', once the Show iTunes Library preference is enabled, under Setup > Library + Display.
If you don't allow this permission you may not be able to successfully import the library from the Music app on your Mac (formerly known as iTunes) into Serato DJ Pro & Lite.
You may also see the following error message:
If you're using a version of Serato DJ Pro or Lite prior to 3.2.1, or you've disabled the permission previously, you may not see the error message above, and your media library may not import correctly, or at all.
Enable Media & Apple Music permission
To resolve this, navigate to and enable the following permission:
System Settings → Security & Privacy → Media & Apple Music → Serato DJ Pro (or DJ Lite)
In some cases you may need to add the relevant application, before it can be enabled, by clicking the + button, and locating Serato DJ Pro or Lite.