I installed Picard on Linux yesterday and went through doing some organization. I’m having trouble with an album that MusicBrainz thinks is spread across two releases (Propellerheads’ “Decksandrumsandrockandroll”), so I saved everything, closed Picard, and reopened it. Now, even though I see all the files for this album in their expected location in Dolphin, Picard’s file browser shows nothing in the album’s directory. What’s going on?
You probably moved the files to a different folder. See Options/File Naming. There you can specify where to save the renamed files.
What do the permissions look like on the folder and files?
Do you have installed Picard as a Flatpak or Snap package? Both packaging formats put the application into a sandbox without direct access to the file system.
By default on both formats Picard has access to your home folder. For snap you can give Picard additional access to “removable media” (or what snap considers as such). See the notes on Download & Install Picard — MusicBrainz Picard v2.13.3 documentation.
For Flatpak it is possible to give access to arbitrary additional folders. Have a look at Flatseal for doing so, or use the command line. See also https://askubuntu.com/questions/1086529/how-to-give-a-flatpak-app-access-to-a-directory
I have installed Picard through Arch’s package manager, so neither Flatpak nor Snap. Picard seems to have all the permissions it needs, since it moved all my files from one drive to another all by itself (which was surprising). I think this is ultimately what the cause was - in the file browser I was looking in the original location, but since Picard had moved things to my home directory, the files were no longer there.