Can’t save file information on MacOSX. Save icon is blank.
If the save icon is disabled it usually means there is no file selected that could be saved.
If you have a track in the right pane that shows just a musical note icon that means this is just data loaded from MusicBrainz, but without a file matched to it. If you have a file for this track, you have to load it into Picard and match it to the loaded track, e.g. by dragging and dropping it.
Can you share a screenshot?