Can't import songs into Music app under Catlina
I found that under Catalina I can't add music to my Music library by either drag and drop of a file or folder of mp3s, or by File>Import.
Even when the song plays normally in the Finder.
Importing worked via either of the first two methods under Big Sur.
However a work-a-round for me was to drop the files/folder in the folder named "Automatically Add to Music" in the Media Folder.
When Music is running, the dropped files disappear form "Automatically..." and are put into the location specified in the Music app Preferences>Files>Media Folder Location. That probably assumes the box "Copy files to Music Media Folder ...." is checked.