Fortigate negotiating on port 853 despite DNS over TLS is disabled

Hello,

We have implemented a vulnerability scanner in our organization, which has detected, among other things, that our FortiGates are listening on port 853 and are presenting themselves with a certificate, which is called "Fortinet_Factory" in the Fortigate web UI. Could you tell me if it is normal that this port is open despite the fact that DLS over TLS is disabled on the device? What other service could be listening on this port? The policy of my organization is to remove all vulnerabilities, so a vulnerability related to the fact that a certificate is not recognized or that a negation has occurred using a set of ciphers considered by the scanner as insecure must be eliminated. Thank you in advance for your help