As at the moment, the Jira Comments component is taking the information of the comment body internally. In case there is an embedded attachment in the comment, it has to pass the requirement that the user is a Jira User, else they won't be able to access the attachment.
But, Jira Service Desk customers are able to see the attachment in the portal view as long it is embedded without Jira User access. With the current limitation of the connector where it takes only the comment body internally, the attachment will not accessible for the Portal Customers.
Hence, it will be great if the connector supports the Portal Comments so the attachments are accessible for the Portal Customers.