Hi Anu,
I have found few issues there. The media mime types were not correctly entered, I have entered pdf, txt and office files to index, now the indexing finished without problems: https://i.imgur.com/tNq8lOq.png
On the instance options, the Index Table engine was not selected either, I have selected that as well: https://i.imgur.com/oQV9HNP.png
It should be returning them now.
For all the details, please check Media Attachment Content indexing documentation.