Okay, seems I made a slight bobo. Should have been 3rd line from the bottom. Try this:
xml:
<variable name="ListBoxInfoVar">
<value condition="String.IsEqual(Container.FolderPath,addons://outdated/) + !String.IsEmpty(ListItem.Addonnews)">$INFO[ListItem.Addonnews]</value>
<value condition="Container.Content(addons)">$INFO[ListItem.AddonDescription]</value>
<value condition="String.IsEqual(listitem.dbtype,album)">$INFO[ListItem.Property(album_description)]</value>
<value condition="String.IsEqual(listitem.dbtype,musicvideo) | String.IsEqual(listitem.dbtype,video)">$INFO[ListItem.Genre,[COLOR button_focus]$LOCALIZE[515]: [/COLOR],[CR]]$INFO[ListItem.Plot]</value>
<value condition="String.IsEqual(listitem.dbtype,artist)">$INFO[ListItem.Property(artist_description)]</value>
<value condition="!String.IsEmpty(ListItem.PlotOutline)">$INFO[ListItem.PlotOutline]</value>
<value condition="!String.IsEmpty(ListItem.Plot)">$INFO[ListItem.Plot]</value>
<value condition="String.IsEqual(ListItem.DBType,song) + !Window.IsActive(musicplaylist)">$VAR[MusicTrackInfo,[COLOR button_focus]$LOCALIZE[554]: [/COLOR],[CR]]$INFO[ListItem.Artist,[COLOR button_focus]$LOCALIZE[557]: [/COLOR],[CR]]$INFO[listitem.Album,[COLOR button_focus]$LOCALIZE[558]: [/COLOR],[CR]]$VAR[InfoDiscVar,[COLOR button_focus]$LOCALIZE[427]: [/COLOR],[CR]]$INFO[ListItem.Year,[COLOR button_focus]$LOCALIZE[345]: [/COLOR],[CR]]$INFO[ListItem.Genre,[COLOR button_focus]$LOCALIZE[515]: [/COLOR],[CR]]$INFO[ListItem.Duration,[COLOR button_focus]$LOCALIZE[180]: [/COLOR],[CR]]$INFO[ListItem.Playcount,[COLOR button_focus]$LOCALIZE[567]: [/COLOR],[CR]]$INFO[ListItem.LastPlayed,[COLOR button_focus]$LOCALIZE[568]: [/COLOR],[CR]]$INFO[ListItem.Comment,[COLOR button_focus]Comment: [/COLOR]]</value>
<value condition="String.IsEqual(ListItem.DBType,song) + Window.IsActive(musicplaylist)">[COLOR button_focus]$LOCALIZE[31037]: [/COLOR]$INFO[Container.CurrentItem,,/]$INFO[Container.NumItems][CR]$VAR[MusicTrackInfo,[COLOR button_focus]$LOCALIZE[554]: [/COLOR],[CR]]$INFO[ListItem.Artist,[COLOR button_focus]$LOCALIZE[557]: [/COLOR],[CR]]$INFO[listitem.Album,[COLOR button_focus]$LOCALIZE[558]: [/COLOR],[CR]]$VAR[InfoDiscVar,[COLOR button_focus]$LOCALIZE[427]: [/COLOR],[CR]]$INFO[ListItem.Year,[COLOR button_focus]$LOCALIZE[345]: [/COLOR],[CR]]$INFO[ListItem.Genre,[COLOR button_focus]$LOCALIZE[515]: [/COLOR],[CR]]$INFO[ListItem.Duration,[COLOR button_focus]$LOCALIZE[180]: [/COLOR],[CR]]$INFO[ListItem.Playcount,[COLOR button_focus]$LOCALIZE[567]: [/COLOR]]</value>
<value>$INFO[ListItem.Genre,[COLOR button_focus]$LOCALIZE[515]: [/COLOR],[CR]]</value>
</variable>
I didn't have any song comments to test with, but I tested by removing the item before (Last Played) and that removed the item from the song I looked at.
Once I made the comment addition, it didn't have any adverse effect elsewhere on my set-up with recently added TV episodes or Kodi not showing the album art. Hopefully, it should work now.