How to import music files like MP3s into Apple Music (iTunes) | Troubleshooting when they won't add

If you want to add music files like MP3s from your PC to iTunes, the basic operation is "Add File to Library." For multiple songs, you can add them by folder. First, try importing them without moving ...
Ars Technica

iTunes permissions problem; Disk Utility can't fix

ACL found but not expected on "Library/iTunes". Repaired "Library/iTunes". If I run Repair Permissions again, I get the same log. So clearly it's not being fixed. And the core symptom (can't sync) ...