- I renamed the Applications folder as you suggested.
- I restarted the system. When I checked the ~/.local/share directory, I had no Applications folder.
- I opened Nautilus>Edit>Preferences>Media and, lo and behold, all the options were available.
- I chose the appropriate applications for each (CD Audio, DVD Video, Music Player, Photos, Software, and some of the other Media) and closed the Preferences dialog.
- I then checked ~/.local/share and an Applications folder had been created with a new mimeapps.list file that only contained the x-content lines, and they were all correct.
- I renamed the mimeapps.list file in the old Applications folder.
- I copied the new mimeapps.list file to the old Applications folder.
- I renamed the the new Applications folder and renamed the old Applications folder back to Applications.
- I restarted the system.
- I checked the Applications menu and my old menus and items where all present.
- I opened Nautilus>Edit>Preferences>Media and every option was as I had set it in step 4 above except Music Player which was grayed out with the message "No applications found".
- I opened the mimeapps.list file and all the x-content lines were there and were correct.
So I have all of my options back except Music Player. The odd thing is, if I choose "Open with other Application" in any of the other options such as CD Audio, my players all show as available to choose. Rhythmbox, Exaile, Quod Libet, VLC, etc. are all there.
So where is the system indicating that there are no apps for Music Player?