Cannot import an MP3 to the Music app
I use the Music app (I guess it was previously named iTunes) for many years. Recently I upgraded to a new MacBook Pro with MacOS 11.2.3 BigSur, I successfully copied my library so it sounds well, but now I'm not able to add new music files to my library :( Whether I click on a file "Open with Music.app" or just drag it to the app or use the Import command from the app (Cmd+O), I get just nothing, no new track in my library, nor error message, just silence... What's wrong here? How this behaviour can be fixed so I can easily import MP3 files again?
PS: the mp3 file is correct of course, I've created it the same way as the old ones in my library, and it get opened fine with QuickTime and other players. But not with the Music app...