When printing a Royal Mail label via Linnworks, the 2D Confirmation code is submitted to the selling channel as a tracking number.
In order to prevent Linnworks from saving the 2D Confirmation code as a tracking number for all Royal Mail labels, the option needs to be disabled for each Royal Mail service. This can be configured within the Shipping > Integrations > Royal Mail > Services screen. Pressing Edit next to a particular service will bring up the service options screen.
Disabling the 2D Tracking Number option on this screen would then prevent Linnworks from saving the 2D Confirmation Code as a tracking number and, as a result, it will not be submitted to the selling channel along with the dispatch notification.
Note that even with this option disabled, it is still possible to see the actual 2D Confirmation code from the Royal Mail manifest screen. This can be accessed by proceeding to Shipping > Shipping Manifests screen for manifests that have not been filed yet, or to Shipping > Filed Manifests for archived manifests, and pressing View next to the Royal Mail field. This will open the View Consignments screen. Pressing the View button on this screen would bring up the properties of a particular order, displaying the DataMatrixEyeReadable field, which is where the 2D confirmation code is stored.
More details about 2D delivery confirmation codes can be found here.