How to search for attachments with the file description
The search for attachments with a file description is a bit different from the individual messages search and you actually can search them with a specific prefix.
To do this, you need to search with the prefix: file-desc: followed by your-file-title
There is an exception to this type of search, you must not include space and you should type only one word which is part of the description, or a few characters(or syllable) which is part of any word inside the file description (see the above screenshot for better clarity).
At the time of writing this article, the only supported language for this is English. However, the Product team is aware of this limitation and working on a fix.