Final Fantasy XIV Online has a community created custom launcher called XIVLauncher to add mod support, however the Steam Recording does not record the game when you launch the game through the XIVLauncher (through Steam), and it will just record a black screen.

If you switch your Game Recording settings from 'Record in background' to 'Off/Don't Record' and then back to 'Record in background', you will get a notification below the timeline that says 'Recording other game'. When you click that it will correctly record Final Fantasy XIV Online.

I understand this is a specific case but it would be nice if Steam Recording could detect it has been recording a black screen for a while after launch and give a notification.