Exactly. No Update notification needed when you already run the latest version.
It is fixed (you can play AAC files) as soon as you yourself provide a ffmpeg version that supports AAC to the app. AFAIK the reason you have to do that, and there will be no other solution for it, is the same reason QNAP removed support for AAC and other codecs - to not get sued and not have to pay licensing fees.
To do so, open the app on your QNAP NAS, use the button and provide a ffmpeg version you downloaded. More information can be found in the other thread specific to that issue: