Import into macOS 10.15 Catalina's Apple Music does not work: unknown error -54; likely root cause: file access permissions

The following procedure removed the problem:

  1. In Finder, select /Users/myaccount/Music/iTunes, the "Get Info".
  2. Current permissions are me: Read & Write, system: Read & Write, wheel: Read only, everyone: Read only. (I apparently mad a mistake in the earlier observation that only me had Read & Write permission there.)
  3. Select "Apply to enclosed items".