Welcome to the Airtable community!
If you have a pro subscription, you can set field permissions so that those users can only edit the attachment field. You will have to manually turn off the ability to edit the other fields one by one, so it is a bit of a pain.
Or if your users are not Airtable collaborators, you can use an Airtable form that creates a new record. Option 1: have the form create a new linked record and always use the latest record. Option 2: use a script that copies the new attachment from the record created by the form to the original record.