Teasing,
Below are 6 different ways to add an audio file to your iTunes/Music library. Once you are sure the valid file is on your local drive, see if at least one will work:
- Drag it into iTunes (or Music)
- Drag it into a specific playlist (i.e., the open window of a regular playlist, not a smart playlist)
- Drag it into the "Automatically Add..." folder
- Use the command File > Import and navigate to its location
- Right-click the MP3 and choose Open With > iTunes (or Music)
- Double-click the MP3
If none of them work you may have an invalid or corrupt file.