Apex domains cannot have CNAME records.
Question and response
Question
dig 96-27.202.104.184.in-addr.arpa. NS
Answer
96-27.202.104.184.in-addr.arpa. 5 NS ns2.discourse.cloud.
96-27.202.104.184.in-addr.arpa. 5 NS ns3.discourse.cloud.
96-27.202.104.184.in-addr.arpa. 5 NS ns1.discourse.cloud.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0