Hi,

That is the default working of odoo. When you add an attachment, it will be displayed in the chatter section, to shift it to the form view, you need to customise it by adding a field and search the attachment from ir.attachment model and show that.

You can use compute function,

attachment_ids = fields.Many2many('ir.attachment',

                                      compute='_compute_attachments')

def _compute_attachments(self):

    attachment_ids = self.env['ir.attachment'].search([

            ('res_model', '=', self._name),

            ('res_id', '=', self.id)

        ])

        self.attachment_ids = attachment_ids.ids

Now you can see all the attachments in the chatter in many2many field in form.

You can define the new field in the view

Hope it helps