Thank you for your comment.
I know wordpress doesn’t have tags features in Meida Library and I added this feature with my custom Plugin in worpress, here is appearance of my Media Library https://snag.gy/DeG83Y.jpg. The “Blink”,“Cat”, “Orange” Tags are attached to Cat photo and cat photo is attached to JIG gallery (see the link above), in this case I was able to index all Tags in Algolia list in managing index here is the link https://snag.gy/GncuVD.jpg. But, when I uploaded another image in Media Library without attaching to any Gallery, I wasn’t able to Index any of these Tags, please see the follwoing link: https://snag.gy/3W4tfh.jpg for better understanding.
The question is why I am not able to index Tags if there are not attached to any Gallery? if the tags just attached to photos, algolia plugin should able to index these tags.