MP3 files are showing up on the Import screen in LrC v11.0 on Windows.
And the following error is generated if you try to import them -
I normally do not import from folders that have anything but images in them, so I don't know how long this has been going on or what's expected, but I don't believe this is correct. My 10.x installations are gone, so I can't test those, but mp3 files do not appear in the v8.2.1 Import screen.