How to add attachment names to a multi-line text columns?

If you want to turn of the attachment image generation, you can do this on the "Advanced" tab of the target data definition.
This will show a text link with the attachment name instead of the image.

In any way, attachment names are indexed in SharePoint, so you should be able to search for them. (The images should link to the actual attachment.)
(This of course only applies if you migrate the attachments as list attachments.)

We wanted to maintain attachment as image, is there a way to migrate attachment names only to text column.

SharePoint indexes content of attachment but it doesn't seems to index name of attachment

From my testing (and also findings on the internet), attachment names are indexed and searchable. This may of course depend on the SharePoint version.

You can use @AttachmentNames (in a source field of type Formula) to access the names of the attachments separately. (Notes may add STG and EXT attachments for embedded objects and images.)

From my testing (and also findings on the internet), attachment names are indexed and searchable. This may of course depend on the SharePoint version.

You can use @AttachmentNames (in a source field of type Formula) to access the names of the attachments separately. (Notes may add STG and EXT attachments for embedded objects and images.)