@vidyU614 Please note that Files&Documents is something else than attachments. But indeed, the attachments seem not te part of the standard user portal, I wonder why that is.
You can add the attachment section (for example pyCaseAttachmentsTopWrapper or the pzCaseAttachmentsGadget) to the section on which you work. Then you will see the usual attachment-section as it was in UiKit.
However, it will lead to another issue I noticed: The sections pyCaseAttachmentsTopWrapper and pzCaseAttachmentsGadget are in the Theme-Cosmos ruleset (that is good), they refer to pyCaseAttachmentItem, which is also in Theme-Cosmos (also good) but that one refers to pyAttachmentOptions in the three-dots menu which is in UiKit and not in Theme-Cosmos, nor anywhere else. So an error is thrown. I am using Pega 8.6.1