I spoke to the QA team regarding this file and it looks like it is an m4a container. QA was not able to import this file even in iTunes and it is using AAC which is Apple’s file format. Are you able to play this file anywhere or import it into iTunes?
AAC audio files generally have the extension .m4a, and these files are fully supported in Roon.
File with the extension .aac are different, and are most commonly used for ADTS streams. Roon will play back ADTS internet radio streams, but we almost never get asked about local files with this extension, and they’re not something Roon supports right now.
You can see more information about common file extensions on the Wikipedia page for AAC. For now, if you want Roon to import this file, I think your best bet is to convert it to a format Roon supports.